In the arrangement shown, the double pulley has a mass M and the two mass less threads have been tightly wound on the inner (radius =r) and outer circumference (radius R=2r). The block shown has a mass 4 M. The moment of inertia of the double pulley system about a horizontal axis passing through its centre and perpendicular to the plane of the figure is I = Mr^2. (a) Find the acceleration of the center of the pulley after the system is released.