A cord is used to lower vertically a block of mass M,a distance d, at a constant downward acceleration $g/4$. Then work done by cord on block

Question

\[(a)\;\frac{-3Mgd}{4} \quad (b)\;\frac{Mgd}{4} \quad (c)\; \frac{3Mgd}{4} \quad (d)\;Mgd\]