Thread: River Current Word Problem

I've been given this word problem for an assignment, and unfortunately I've forgotten the procedure for solving the problem. A solution would be greatly appreciated.

Jane paddles her canoe at a rate of 15km/h in still water.
One day she paddles 40km upstream to her destination, and immediately paddles 40km back downstream.The total trip takes her 6 hours to complete.
What is the speed of the river current?

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-Dan