A student drops two metallic objects into a 120 g steel container holding 150 g of water at 25°C. One object is a200 g cube of copper that is initially at 75°C, and the other is a chunk of aluminium that is initially at 5.0°C. To the surprise of the student, the water reaches a final temperature of 25°C, precisely where it started. What is the mass of the aluminium chunk?