A small motorboat travels 12mph in still water. It takes 3 hours longer to travel 68 miles going upstream than it does going downstream. Find the rate of the current.

Let the speed of the current be x mi/hr

speed upstream = (12-x) mi/hr

speed downstream = (12+x) mi/hr

It takes 3 hours longer to travel upstream than downstream, thus

time taken upstream=68 / (12-x)

time taken to travel downstream=68 / (12+x)

the difference in time will be:

68 / (12-x) - 68 / (12+x) = 3

solving for x we get:

x=2.98 mi/hr

Thus the rate of current is 2.98 mi/hr