Answer
$$K_c = \frac{[CO][H_2]^3}{[CH_4][H_2O]} $$
Work Step by Step
$$K_c = \frac{[Products]}{[Reactants]}$$
$$K_c = \frac{[CO][H_2]^3}{[CH_4][H_2O]} $$
** Since there are 3 $H_2$ molecules in the balanced equation, we have to put in a "3" as the exponent of $[H_2]$.