Four spheres of diameter 2a and mass M are placed with their centres on the four corners of a square of side b. Then the moment of inertia of the system about an axis along one of the sides of the square is

Question

$$\begin {array} {1 1} (a)\;\frac{4}{5}Ma^2+2 Mb^2 & \quad (b)\;\frac{8}{5}Ma^2+2 Mb^2 \\ (c)\;\frac{8}{5}Ma^2+Mb^2 & \quad  (d)\;\frac{4}{5}Ma^2+4Mb^2 \end {array}$$