A girl is skipping rocks across a lake. One of the rocks accidentally ricochets off a toy boat initially at rest in the water. The 0.086 kilogram rock strikes the boat at a velocity of 13 m/s, 15 degree below due east, and ricochets off at a velocity of 11 m/s, 12 degree above due east. After being struck by the rock, the boat's velocity is 1.2 m/s, due east. Find what is the mass of the boat? Suppose the water offers no resistance to the boat's motion.