For the Equilibrium PCl₅(g) PCl₃(g)+ Cl₂(g),K_c = 4

For the equilibrium PCl₅(g) PCl₃(g) + Cl₂(g) ,K_c = 4.0 at 228°C.If pure PCl₅ is placed in a 1.00-L container and allowed to come to equilibrium,and the equilibrium concentration of PCl₅(g) is 0.26 M,what is the equilibrium concentration of PCl₃?

A) 0.13 M
B) 0.37 M
C) 0.26 M
D) 1.0 M
E) 0.017 M