Moment of inertia is highly dependent on the how the mass is distributed about the axis of rotation. If more mass is further away, then the moment of inertia is greater than if the mass is closer to the center of rotation. I don't have your text book, but I'm guessing that it is probably a rectangular shape with three different dimensions of height, width, and length. It probably has three axes of symmetry  do you know what they are? Which axis of symmetry gives the smallest values of distance to the furthest edge or corner?
