$******9\mathrm{.}3\mathrm{.}34.$ In one stage of a process for the manufacture of liquid air, air as a gas at $4$atm absolute and $250K$ is passed through a long, insulated $3-$in$.-$ID pipe in which the pressure drops $3$ psi because of frictional resistance to flow. Near the end of the line, the air is expanded through a valve to $2$atm absolute$.$ State all assumptions.

a$.$ Compute the temperature of the air just downstream of the valve.

b$.$ If the air enters the pipe at the rate of $100l\frac{b}{h}r,$ compute the velocity just downstream of the valve.