Help! Urgent, Heat transfer question :)?

Hot water is to be used in a room heater, entering the heater at 80�C and leaving at 50�C, to maintain the air in the room at 20�C. To achieve this, the required heat transfer rate is 1.0 kW. The predicted overall heat transfer coefficient based on the outside area of the heater surface is 20 W m-2 K-1. Calculate the log mean temperature difference for heat transfer. Key in your answer with two significant figures.