Shawn can paddle his canoe at a rate of 7 miles per hour in still water. He travels 45 miles upstream and 45 miles downstream in a total time of 14 hours. What is the speed of the current?

let speed of current = xmiles/hr

downstream: speed = 7+x

upstream: speed = 7-x

total time:

 = 45/(7+x)  +  45/(7-x)

=> 14 = 45/(7+x) + 45/(7-x)

=> -X^2 + 49 = 45

=> x^2 = 4

=> x = 2 miles/hr