Question

a boat takes 8 hours to go 6 miles upstream and come back to the starting point. if the speed of the boat is 4 miles per hour in still water, what is the rate of the current

Answer 1

 v=d/t; t=d/v 
let c=rate of the current 
6/(4+c)+6/(4-c)=8 
(24-6c+24+6c)/(16-c²)=8 
48=128 - 8c²; c=√10 miles per hour