Question 245506
Let the distance traveled be D and the rate in still water be R.

The effective rate going upstream is R-10 and downstream is R+10.

The distance traveled is the "effective" rate multiplied by the time traveled so:

D = (R-10)*5 going upstream and
D = (R+10)*3 going downsteam 

We have then (R-10)*5 = (R+10)*3

Solve for R to get the rate in still water.