Answer:
 The mass flow rate of steam m=5.4 Kg/s 
Explanation:
Given: 
   At the inlet of turbine P=10 MPa  ,T=500 C
  AT the exit of turbine  P=10 KPa   ,x=0.9
  Required power=5 MW
From steam table 
<u> At 10 MPa and 500 C:</u>
   h=3374 KJ/Kg  ,s=6.59 KJ/Kg-K  (Super heated steam table)
<u>At 10 KPa:</u>
=2675.1 KJ/Kg, 
=417.51  KJ/Kg
= 7.3  KJ/Kg-K                ,
=1.3   KJ/Kg-K
So enthalpy of steam at the exit of turbine
h= 
Now by putting the values
h= 417.51+0.9(2675.1- 417.51) KJ/Kg
h=2449.34  KJ/Kg
Lets take m is the mass flow rate of steam 
So 
m=5.4 Kg/s
So the mass flow rate of steam m=5.4 Kg/s