Need some help with some simple math.

Pot is 200$, we decide to jam 600$ with an estimated 25% equity.

How do I solve for his fold% where our jam is 0EV ?

EV(0) = EVfold * fold% - EVcall * call%
EVfold = 200$
EVcall = 0,25 * 1400 - 600$ = -250

so

EV(0)= 200$ * x - 250 * (1-x) where x is fold% and 1-x is call%

Been away from school for too long, how do we continue with the algebra to solve x ?

Cheers