A boat requires four hours to travel a given distance upstream against a five mile per hour current, but only requires three hours to travel downstream with that same current back to the dock. Find the speed of the boat in still water.

Question

A boat requires four hours to travel a given distance upstream against a five mile per hour current, but only requires three hours to travel downstream with that same current back to the dock.  Find the speed of the boat in still water.

anonymous · Answer

I've gotten part of it, but lose it after a certain point

anonymous · Answer

over four hours with a -5 current, that means you'll travel 20 miles less than you would normally (4*velocity of boat). The other direction means you'll get another 15 miles because of the +5 current. Same distance both ways, so they're equal.
4v-20=3v+15
v=35mi/hr.