<p>This is from AMC 2011. </p>

<p>A power boat and a raft both left dock A on a river and headed downstream. The raft drifted at the speed of the river current. The power boat maintained a constant speed with respect to the river. The power boat reached dock B downriver, then immediately turned and traveled back upriver. It eventually met the raft on the river 9 hours after leaving dock A. How many hours did it take the power raft to go from A to B?</p>

<p>A)3 B)3.5 C)4 D)4.5 E)5</p>