Show me the steps to solve: Problem $4)$ Propane enters a throttle at a pressure of $100$ lbf$/$in$2$ and a temperature of $120\backslash$deg F$.$

After the throttle, the pressure is $60$ lbf$/$in$2.$

a$)$ What is the enthalpy after the throttle?

b$)$ What phase of mater is the propane after the throttle?