class RentalUnit {
  constructor(address, costPerYear) {
    this._address = address;
    this._costPerYear = costPerYear;
  }
 
  get address() {
    return this._address;
  }
 
  get costPerYear() {
    return this._costPerYear;
  }
 
  calculateMonthly() {
    return this.costPerYear / 12; 
  }
}
 
class Apartment extends RentalUnit {
  constructor(address, costPerYear, numberOfBedrooms) {
    super(address, costPerYear);
    this._numberOfBedrooms = numberOfBedrooms;
  }
 
  get numberOfBedrooms() {
    return this._numberOfBedrooms;
  }
}