A man in a rowing away from light house 100 m high takes 2 minutes to changes the angle of elevation of the top of light house from 60 degree to 45 degree find the speed of the boat?

At the start his distance from the lighthouse is 100/tan(60) = 86.6 m.

After 2 minutes his distance from the lighthouse is 100/tan(45) = 70.7 m.

He travels 15.9 m in 2 minutes = 7.9 m per minute.