Phosphorous Trichloride and Phosphorous Pentachloride Equilibrate in the Presence of Molecular

Phosphorous trichloride and phosphorous pentachloride equilibrate in the presence of molecular chlorine according to the reaction:
PCl₃ (g) + Cl₂ (g) -PCl₅ (g)
An equilibrium mixture at 450 K contains P_PCl3 = 0.202 atm,
P_Cl2 = 0.256 atm, and
P_PCl5 = 3.45 atm. What is the value of K_p at this temperature?

A) 1.50 × 10^{- 2}
B) 66.8
C) 2.99
D) 7.54
E) 1.78 × 10^{- 1}