4{C3H5(NO3)2}(l)--->6N2(g)+O2(g)+12CO2(g)+10H2O(g)

Question

If a dynamite of 100mL needs 3.5atm to explode, what minimum mass of
C3H5(NO3)2 do I need to put in at 25 degree celcius?
I tried to do this by finding the number of moles by the formula PV=nRT and then convert that into masss.is this correct?
if not please explain why.

thanks in advance!