I can't understand why at last question of module 3 we received 30 how? Please answer me

Answer 1

In the Main Methode you call the method Test an pass in a as a Reference.
In the First line of The Test Method the Variable x wich Points to a get assigned with 6, now the Variable a in Main method has now also the value 6. in Second line of Test you calculate 6(x) * 4(default value y).
Test returns 24 and z in Main method gets assigned. At Last you Print 24+6 ->30

Answer 2

I think it return to type of parameters with out type there