Struggling to Solve this one

class Student {
    constructor(gpa, credits, major){
        this.gpa = gpa;
        this.credits = credits;
      this.major = major;
    }

    stringGPA() {
        return this.gpa.toString();
    }
  set major(major){
  if( major ==='Senior' || major ==='Junior'){
    this.major = major;
  }else if ( major ==='Freshman' || major ==='Sophomore'){
  this.major ="None";
  }

    get level() {
        if (this.credits > 90 ) {
            return 'Senior';
        } else if (this.credits > 60) {
            return 'Junior';
        } else if (this.credits > 30) {
            return 'Sophomore';
        } else {
            return 'Freshman';
        }
    }
}

var student = new Student(3.9, 60);
Student.major = Student.level;