Equilibrium Concentrations in a Gas Reaction

Consider the following reaction reaching equilibrium:

A (g) + B (g) <=> C (g) + D (g)

The equilibrium constant (K_c) for this reaction at a certain temperature is 4.0. If the initial concentrations of A and B are both 1.0 M, and no C or D is present, what would the equilibrium concentrations of C and D be if the change in concentration for the formation of C and D is represented as 'x'?