The apparent equilibrium constant for the reaction

A + B <==> 2C

is Kc= 4.11 at 298.2 K. Given that the initial concentrations of A, B, and C are .10M, .10M, and zero, respectively, find the equilibrium concentrations of A, B, and C.

I had this long, drawn out equation written up that I solved using the quadratic formula, but it didn't yield the correct answer so I'm assuming I went about it the wrong way. How would I solve this?

You solve it with the long drawn out equation, from this relationsip.

Kc= [2x]^2 /(.1-x)^2