The current in a river is 4 mph. A boat can travel 18 mph in still water. How far up the river can the boat travel if the round trip is to take 10 hours?
Options:	A) 69 miles	B) 85.5 miles	C) 96 miles	D) 100 miles	E) 112 miles

Rationale: "upstream speed = 18 - 4 = 14 mph downstream speed = 18 + 4 = 22 mph d / 14 + d / 22 = 10 hours solving for d we get d = 85.5 answer : b"
Answer: B