Calling the mass of a single brick m, then the mass of the N−1 bricks is (N−1)m, and the center of mass of the bottom brick is 12L farther from the origin than the center of g...Calling the mass of a single brick m, then the mass of the N−1 bricks is (N−1)m, and the center of mass of the bottom brick is 12L farther from the origin than the center of gravity of the N−1 bricks. [For a reminder of how to find the center of mass of two extended objects with their own centers of mass, go here.]