Ricardo, mass 80 kilogram, and Carmelita, who is lighter, are enjoying Lake Merced at dusk in a 30 kilogram canoe. When the canoe is at rest in the placid water, they exchange seats, which are 3.0 meter apart and symmetrically placed with respect to the canoe's center. Ricardo notices that the canoe moved 50 centimeter relative to a submerged log during the exchange and determine Carmelita mass, which she has not told him. What is it?