On a warm summer day (30°C), it takes 4.80 s for an echo to return from a cliff across a lake. On a winter day, it takes 5.20 s. The speed of sound in air is $v \approx (331 + 0.60T)$ m/s, where $T$ is the temperature in °C. What is the temperature on the winter day? Express your answer to two significant figures and include the appropriate units.