Rate.cs

class Rate : IRate {
  
  public Rate(CustomerType, weekdays, weekdayPrice, weekendPrice) {
    // .....
  }
  
  public double calculte (Days days...) {
    double totalPrice = 0;
    for(var day in days) {
      if day is weekdays {
        totoalPrice += weekdayPrice;
      } else {
        totalPrice += weekendPrice;
      }
      
    }
    return totalPrice;
  }

}

public enum Day {
  Mon = 1
  Tue = 2
  Wed = 4
  Thu = 8
  Fri = 16
  Sat = 32
  Sun = 64
}

IRate rate = new Rate(CustomerType.Regular, Day.Mon | Day.Tue | Day.Wed, 100, 200);
rate.calculate(Day.Mon | Day.Tue | Day.Wed);