Steam enters an adiabatic turbine at $500$ psia and $900F$ at a flow rate of $480f\frac{t^3}{m}in.$

Expansion in the turbine leads to an exit pressure of $20$ psia. Calculate the turbine

power output $($in $hp)$ if the

a$)$ Temperature at the turbine exit is $280F$

b$)$ Expansion process is reversible