20 cubic inches of a gas with an absolute pressure of 5 psi is compressed until its pressure reaches 10 psi. what's the new volume of the gas? (assume that there's no change in temperature.)

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

Ithink it's carbonic acid