Physical Pendulum Period Modification

A physical pendulum with a mass of $M = 2.0\ \mathrm{kg}$ has a moment of inertia $I = 0.5\ \mathrm{kg\cdot m^2}$ about its pivot point. The distance from the pivot to the pendulum’s center of mass is $d = 0.3\ \mathrm{m}$. When a small mass $m$ is attached to the pendulum at a distance $r = 0.4\ \mathrm{m}$ from the pivot, the period of oscillation doubles. What is the value of the attached mass $m$?