How to set the Values of dependent variables

I want to solve a pair of equations which are based on other two study steps, but in the setting of the "values of variables not solved for", I can only choose on study( and i actuallly want to add two study). How do I pass the solved value of the varibles into the equations that I try to solve subsequently? For example, I first solve a pair of question to get the Value of U and V, then I solve another equation to get the value of p, the finally I want to solve w and k, whose equations involve with U, V and p. How should I pass the value of U, V and p.