could you show me how to solve for x it is killing me

y/x^2 = b/(a-x)^2

Sure.

(a-x)^2/x^2 = b/y
(a-x)/x = sqrt(b/y)= (a/x) - 1
a/x = sqrt(b/y) + 1
x = a /[sqrt(b/y) + 1]