my solution :

let products = [
    {
        name : 'tuna',
        inventory : 4,
        unit_price : 8.60
    },

    {
        name : 'Salmon',
        inventory : 10,
        unit_price : 5.60
    },
];

function listProducts(obj) {
    let objName = [];
    for (i = 0; i < obj.length; i++) {
        let indexName = obj[i].name;
        objName.push(indexName);
    }
    console.log(objName);
    return objName;
}

listProducts(products);

function totalValue(arr) {
    let totalVal = 0;
    for (i = 0; i < arr.length; i++) {
        arrVal = arr[i].inventory * arr[i].unit_price;
        totalVal += arrVal;
    }
    console.log(totalVal);
    return totalVal
}

totalValue(products);