How do you solve an equation with 2 unknowns that equal the same?

A single equation with two variables can be solved for one of the variables, in terms of the other. For example, a rectangle's area is A = wh (width x height). Now let's assume you know the area: 20 = wh. You can solve for any of these variables in terms of the other, for example, w = 20/h. That is, once you assign a value to "h", you can calculate "w". But you don't know the specific values for "w" and "h", because the equation has an infinite number of solutions.

If you want to know specific values for the variables, in general, you need two different equations with 2 variables - or 3 equations with 3 variables, etc.