I need to reduce the diagram, when each input is 0, I can do when d=0, however i'm finding it a little difficult when r=0.
I have solved the exercise using a signal flow diagram and the solution is written here, i'm not getting the same result from block reduction.
It might help if you rearrange the block diagram a little, namely the first is represented with
which after some shifting around it is equivalent to
It can also be solved by introducing some temporary variables, usually defined after summation nodes and then solve a system of linear equations. This would allow you to simultaneously solve for $C(s)$ as a function of $R(s)$ and $D(s)$.