Equilibrium: JEE Main 2006 Chemistry question

Phosphorus pentachloride dissociates as follows, in a closed reaction vessel PCl₅ (g) $\leftrightharpoons$ PCl₃ (g) + Cl₂ (g) If total pressure at equilibrium of the reaction mixture is P and degree of dissociation of PCl₅ is x, the partial pressure of PCl₃ will be