The current in a river is 3 mph. A boat can travel 21 mph in still water. How far up the river can the boat travel if the round trip is to take 10 hours?
Pick one:
A) 69 miles B) 88 miles C) 96 miles D) 102.8 miles E) 112 miles

Rationale: "upstream speed = 21 - 3 = 18 mph downstream speed = 21 + 3 = 24 mph d / 18 + d / 24 = 10 hours solving for d we get d = 102.8 answer : d"
Answer: D