A river flows due south with speed of 2.0m/s. a man steers a motorboat across the river. the river is 800m wide. at what angle in the counterclockwise direction, measured from an axis aligned with the bank of the river and pointing south, should the motorboat head in order to reach a point on the opposite bank directly east from the starting point? (the boat's speed relative to the water is 4.0m/s)
a) 30 deg
b) 60 deg
c) 90 deg
d) 120 deg
e) 150 deg