10 cubic inches We will use Boyle's law that states that for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional. P1 V1 = P2 V2 Where P1 is initial pressure = 5 psi V1 is initial volume = 20 cubic inch P2 is final pressure = 10 psi V2 is final volume = unknown V2 = P1,V1 / P2 V2 = 20 × 5 / 10 V2 = 100/10 V2 = 10 cubic inches