Answer : The equilibrium constant for the reaction will be, 
Explanation :
The following equilibrium reactions are :
(1)

(2)
The final equilibrium reaction is :

Now we have to calculate the value of
for the final reaction.
First we have to multiply equation (1) by 2 that means we are taking square of equilibrium constant 1 and reverse the equation 2 that means we are dividing equilibrium constant 2, we get the final equilibrium reaction and the expression of final equilibrium constant is:

Now put all the given values in this expression, we get :


Therefore, the value of
for the final reaction is, 