A certain fluid at 15 psia is contained in a cylinder behind a frictionless piston. The initial volume of the fluid is 300 in^3. The fluid expands to a volume of 450 in^3 while the pressure increases to 25 psia. Assume the pressure increased linearly with volume, and that the fluid expansion was fully resisted. The work done by the fluid (system), in ft*lbf, is?