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 ?
"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"
divide(multiply(multiply(subtract(18, 4), add(18, 4)), 10), add(add(18, 4), subtract(18, 4)))