A thin uniform square lamina of side a is placed in the xy-plane with its sides parallel to x and y-axes and with its center coinciding with origin. Its moment of inertia about an axis passing through a point on the y-axis at a distance $y=2a$ and parallel to x-axis is equal to its moment of inertia about an axis passing through a point on the x-axis at a distance $x=d$ and perpendicular to xy-plane. Then value of d is :
