The combined gas law states that
PV
T
= C, where P, V, and T are the pressure, volume, and temperature of a gas, and C are a constant.

Avogadro's Law says that the constant C is directly proportional to the amount of gas, n (moles), where the proportionality factor R is the universal gas constant. So, C = nR.

From these two laws, we can derive the Ideal Gas Law, which is

a p=VnRT
b PV=nRT
c P=v/nRT
d PV=nR/T