Use of unresolved identifier totalPrice? what's wrong

@IBOutlet weak var collectionView: UICollectionView!
@IBOutlet weak var totalLabel: UILabel!
@IBOutlet weak var balanceLabel: UILabel!
@IBOutlet weak var quantityLabel: UILabel!
@IBOutlet weak var priceLabel: UILabel!


@IBOutlet weak var quantityStepper: UIStepper!


let vendingMachine:VendingMachine
var currentSelection:VendingMachine?//to store the selection

required init?(coder aDecoder: NSCoder) {
    do{
        //use type methods,take plist and cinvert it to dictionary
        let dictionary = try PListConverter.dictionary(fromFile: "VendingInventory", ofType: "plist")
        //once we have a dict we can fgo and create an inventory
        let inventory = try InventoryUnarchiver.vendingInventory(fromDictionary: dictionary)
       self.vendingMachine = FoodVendingMachine(inventory: inventory)

    }catch let error{
        fatalError("\(error)")
    }
    super.init(coder: aDecoder)
}




override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    setupCollectionViewCells()
    balanceLabel.text = "$\(vendingMachine.amountDeposited)"
    totalLabel.text = "$00.00"
    priceLabel.text = "$0.00"    }

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

// MARK: - Setup

func setupCollectionViewCells() {
    let layout = UICollectionViewFlowLayout()
    layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 20, right: 0)

    let padding: CGFloat = 10
    let itemWidth = screenWidth/3 - padding
    let itemHeight = screenWidth/3 - padding

    layout.itemSize = CGSize(width: itemWidth, height: itemHeight)
    layout.minimumLineSpacing = 10
    layout.minimumInteritemSpacing = 10

    collectionView.collectionViewLayout = layout
}

//MARK:- Vending

@IBAction func purchase() {
    if let currentSelection = currentSelection{

        do{
            try vendingMachine.vend(selection: currentSelection as! VendingSelection, quantity:Int(quantityStepper.value))
            updateDisplayWith(balance: vendingMachine.amountDeposited,totalPrice:0.0,itemPrice: 0,itemQuantity:1)
        }catch{
            //error handling code 
        }
        if let indexPath = collectionView.indexPathsForSelectedItems?.first{
            collectionView.deselectItem(at: indexPath, animated: true)
            updateCell(having: indexPath, selected: false)
            quantityStepper.value = 1 //everytime we select a new item the quantity goes back to 1 (whenever an item is selected)
            quantityLabel.text = "1"
           // quantity = 1

        }

    }else{
        //alert user to  no selection
    }
}
func updateDisplayWith(balance: Double? = nil, totalPrice? = nil,itemPrice:Double? = nil,itemQuantity : Int? = nil){

    if let balanceValue = balance {

    if let totalValue = totalPrice{

    if let priceValue = itemPrice{
      priceLabel.text = "$\(priceValue)"
    }

    if let quantityValue = itemQuantity{
        quantityLabel.text = "$\(quantityValue)"
    }

}

func updateTotalPrice( for item : VendingItem){
    totalLabel.text = "\(item.price * quantityStepper.value)"
}


@IBAction func updateQuantity(_ sender: UIStepper) {

    quantityLabel.text = "\(Int(quantityStepper.value))"

    if let currentSelection = currentSelection,let item = vendingMachine.item(forSelection: (currentSelection as? VendingSelection)!){
        updateTotalPrice(for: item)
    }
}


// MARK: UICollectionViewDataSource


func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return vendingMachine.selection.count
}


func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as? VendingItemCell else { fatalError() }
    let item = vendingMachine.selection[indexPath.row]//inddex value is stored into index path
    cell.iconView.image = item.icon()
    return cell
}

// MARK: - UICollectionViewDelegate

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    updateCell(having: indexPath, selected: true)

    quantityStepper.value = 1
    quantityLabel.text = "1"
   // quantity = 1
    totalLabel.text = "$00.00"







    currentSelection = vendingMachine.selection[indexPath.row] as? VendingMachine
    if let currentSelection = currentSelection,let item = vendingMachine.item(forSelection: (currentSelection as? VendingSelection)!){


        priceLabel.text = "$\(item.price)"
        totalLabel.text = "$\(item.price * quantityStepper.value)"
    }
}

func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
    updateCell(having: indexPath, selected: false)
}

func collectionView(_ collectionView: UICollectionView, didHighlightItemAt indexPath: IndexPath) {
    updateCell(having: indexPath, selected: true)
}

func collectionView(_ collectionView: UICollectionView, didUnhighlightItemAt indexPath: IndexPath) {
    updateCell(having: indexPath, selected: false)
}

func updateCell(having indexPath: IndexPath, selected: Bool) {

    let selectedBackgroundColor = UIColor(red: 41/255.0, green: 211/255.0, blue: 241/255.0, alpha: 1.0)
    let defaultBackgroundColor = UIColor(red: 27/255.0, green: 32/255.0, blue: 36/255.0, alpha: 1.0)

    if let cell = collectionView.cellForItem(at: indexPath) {
        cell.contentView.backgroundColor = selected ? selectedBackgroundColor : defaultBackgroundColor
    }
}