A motorboat is moving due east on a calm river. A stationary observer on the shore measures a floating log to drift 2 m/s east relative to the shore. An observer on the boat measures the log to move 6 m/s west relative to the boat. What is the speed of the boat relative to the shore?
a) 4m/s west
b) 8m/s west
c) 8m/s east
d) 4m/s east