Create a struct named `Car` and another one named `RentalBusiness`.
Create a struct named `Car` and another one named `RentalBusiness`.
The scope of the exercise will be to modify and operate on the `Car` in the `RentalBusiness` even if this element is not declared as mutable.
The scope of the exercise will be to modify and operate on the `Car` in the `RentalBusiness` even if this element is not declared as mutable, introducing the concept of interior mutability.
To accomplish that you will create some associated methods of `RentalBusiness` that will return the field `car` in many different ways.