A man is watching from the top of a tower a boat speeding away from the tower. The boat makes an angle of depression of 45° with the man's eye when at a distance of 100 metres from the tower. After 10 seconds, the angle of depression becomes 30°. What is the approximate speed of the boat, assuming that it is running in still water?

• A. 6.28 km/hr
• B. 2.42 km/hr
• C. 4.22 km/hr
• D. 1.25 km/hr