Steady State Error of Control System
Just redraw the diagram like this: -



I've used Y instead of theta for my own convenience.

You get Y = I.G(M - Y.D) which reduces to \$\dfrac{Y}{M} = \dfrac{1}{\frac{1}{G.I} + D}\$

I can see that if you plug the expressions for G, I and D in you get the correct answer.