Here it is
[attachment id=0 msg=2785]

According to the question

A(g) +B(g)   [attachment id=0 msg=2810]   C(g)+D (g)

   A   B   C   D
Initial   2X   X   0   0
Change   -Y   -Y   +Y   +Y
Equilibrium    2X-Y   X-Y   Y   Y
                       3X/2   X/2       X/2       X/2
Now B and C are equal means
X-Y =Y
So X = 2Y
Y=X/2
Plug in  value of Y in final equilibrium

K =[C][D] /[A]
K = (X/2)^2 /3X/2*X/2
Solve it