Question: A man at point A directs his rowboat due north toward point B, straight across a river of width 100 m. The river current is due east. The man starts across, rowing steadily at 0.75 m/s and reaches the other side of the river at point C, 150 m downstream from his starting point.
Question 1: What is the speed of the river?
Please explain your answer. I know substitution is involved so be sure to give a detailed explanation on that as well.