A classical mechanics problem by Md Zuhair

A plank of mass $M$ is placed over a smooth triangular wedge with an angle of inclination $30^\circ$ . A block of mass $m$ is connected to the plank by a massless string . a cylinder of mass $M$ and radius $R$ is now placed over the plank, such that one end of the string , wrapped over cylinder is fixed and parallel to incline . friction is sufficient enough for pure rolling of cylinder. If the system is released from rest with condition that $M=4m$ , find the angular acceleration $\alpha$ of the cylinder .