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
