A rod, AB, of length 5m and mass 12 kg is hanging over the edge of a cliff. The end A is 1.2m from the edge of the cliff, and the rod is assumed to be perpendicular to the cliff. A woman, of mass M, stands at the point A, and a girl, of mass m, stands at the point B. Given that the rod is on the point of tipping, find m in terms of M.