Answer
$Q= 0\ kJ$
$W=25.3\ kJ$ (out)
Work Step by Step
From table A-13:
Initial ($P_1=0.8\ MPa, T_1=50°C$): $s_1=0.9803\ kJ/kg.K,\ u_1=263.87\ kJ/kg$
Final ($P_2=0.14\ MPa, s_2=s_1$): $u_2=227.77\ kJ/kg$
Isentropic process implies $Q= 0\ kJ$
From the energy balance:
$-W=\Delta U=m(u_2-u_1)$
Given $m=0.7\ kg$
$W=25.3\ kJ$ (out)
