According to the ideal gas equation-
PV = nRT
P = n/V x RT
P = CRT where C is molarity
PA = CART = [A] x RT
PB = CBRT = [B] x RT
PC = CCRT = [C] x RT
PC = CDRT = [D] x RT
Put the value of PA, PB, PC and PD in the equation
Kp = [C]c (RT)c [D]d (RT)d / [A]a (RT)a [B]b (RT)b
Kp = [C]c x [D]d / [A]a x [B]b x (RT)c+d-a-b
Kp = Kc x (RT)Δn
Where Δn there is a difference of the number of molecules of the products and the reactants.