4. A swimmer is in distress in Lake Extremis, 180 metres from shore. A lifeguard, standing at the shore line, is 500 metres from the point on shore nearest to the swimmer. If the lifeguard can run at 4 m/s across the sand, and can swim at 2 m/s through the water, what course should the lifeguard take to reach the swimmer in the fastest time? Round final answer to the nearest metre. (9 marks)