Calculating a Constant Pressure process

In a constant pressure, nonflow process, 6Btus of heat are added to a gas while the volumes change from 1.6ft^3 to 2.0ft^3. If the temperature decreases by 10*F and the system contains 2 lbm of gas, find the pressure in the system. (Cv=.2Btu/lbm*F) 1Btu=778 ft-lbm