If the volume is 12 mL at 40 lb/in2, then 1/V = (1/12) mL-1.
If 12 mL refers to the initial volume, V1, of the gas at an initial pressure P1, and then the pressure has been changed to P2 (= 40 lb/in2), you would have to calculate the corresponding new volume V2.
The question you quoted implies there is a data set that you are not showing.
I can not help you any further unless you post the entire question exactly as you have it - as I have already asked.