A glass tumbler of 200 g mass and 5 cm inside diameter is full to a depth of 10 cm with tap water whose temperature is 10 degrees C, and at 50 g of ice 0 degrees C are then added. At the end of an hour, it is noticed that the ice has just finished melting. What was the average rate, in calories per second, at which heat flowed into the glass from its surroundings?