Pardon the handwriting but this is the answer that i got. Taking into consideration that P is a constant, its not wrong to leave it there in any of the expressions. Since P has to be positive integer, it can be any constant. However since H is a value of height, it has to also be positive. Looking at the expression of h, it is the component p minus the component X. So the only way it is true is if the p component is greater than the X component, therefore making h positive. Otherwise, the only domain h needs fulfill is that it is a positive integer.

Hope it helps!