a hollow $($ID$=1\mathrm{.}6$ cm$,$ OD $=2$ cm$),0\mathrm{.}5-$m$-$long, steel $($G$=77$ GPA$)$ shaft AB is attached to a solid $($OD$=2$cm$),0\mathrm{.}25-$m$-$long, brass $(G=39$GPA $)$ rod $BC$ as shown here. This assembly is then rigidly mounted with fixed ends. When a $200N-m$ torque is applied at B$,$

a$)$ What are the reactions at A and $D?$

b$)$ What is the angle of twist of plane B $($in degree$)$

Please fill in the answer for the twist angle of plane B in degree.

The detail of the solution should be in the blue book to get the full credits