Moment of inertia of an equilateral triangular lamina ABC, about the axis passing through its centre O and perpendicular to its plane is Io as shown in the figure. A cavity DEF is cut out from the lamina, where D, E, F are the mid points of the sides. Moment of inertia of the remaining part of lamina about the same axis is :

Question

$ $\begin{array}{1 1}(1)\; \frac{7}{8} I_o \\ (2)\; \frac{15}{16} I_o \\ (3)\; \frac{3}{4} I_o \\ (4)\; \frac{31}{32} I_o \end{array} $