Refrigerent 134a at a flow rate of 0.5 lb/s enters a heat exchanger in a refrigeration system operating at steady state as saturated liquid at 20 degrees Fahrenheit at a pressure of 20lbf/in^2. A separate air stream passes in counter flow to the refrigerant 134a stream, entering at 120 degrees Fahrenheit and exiting at 77 degrees Fahrenheit. The outside of the heat exchanger is well insulated. Neglecting kinetic and potential energy effects and modeling the air as an ideal gas, determine the mass flow rate of air, in lb/s.