One evening Wilson, Xavier, Yeoman, Zenger, and Osborn made separate camps along the banks of a river. The next morning all were to meet at Osborn's camp; then each man besides Osborn was to return to his own camp.

1. Wilson and Xavier camped downstream from Osborn, while Yeoman and Zenger camped upstream from Osborn.
2. Wilson, Xavier, Yeoman, and Zenger each had a motor boat; each motor boat would take its owner to Osborn's camp in one hour, if there were no current in the river.
3. There was a strong current in the river.
4. The next morning each of the four men went in his motor boat to Osborn's camp; Wilson made the trip in 75 minutes, Xavier made the trip in 70 minutes, Yeoman made the trip in 50 minutes, and Zenger made the trip in 45 minutes.

Which one of the four men made the round trip, to and from Osborn's camp, in the shortest time?