please solve this question step-by-step

Owing to a faulty door contact, the small light bulb (25W) inside a refrigerator is kept on and limited insulation lets 50W of energy from the outside seep into the refrigerated space. How much of a temperature difference from the ambient surroundings at 20C must the refrigerator have in its heat exchanger with an area of 1m2 and an average heat transfer coefficient of 15W/m2K to reject the leaks of energy