A foam cooler of negligible mass contains 1.75 kg of water. Ice from a refrigerator at −15°C, is then added to the water in the cooler. When thermal equilibrium has been reached, the total mass of ice in the cooler is 0.778 kg. Assuming no heat exchange with the surroundings, what mass of ice was added? For water, Lf = 334 × 103 J/kg, and for ice, ci = 2100 J/(kg • K).