Unsteady Mass Flow Rate Question?

There is a steady leak of air into the tank at a rate of 0.001 Lbm/min. The furnace contains a total volume of 10 ft^3 of air, which may be considered an ideal gas. The vacuum pump is pumping air out prior to beginning the thermal diffusion step. During the pumpout process the heating coils in the tank hold the temperature in the tank constant at 68F. The volumetric flow rate at the inlet of the pump, independent of pressure, is 1.0 ft3/min. Calculate the final pressure of the system after 60 minutes assuming initial pressure of 1 atm.