A sailboat can travel 60 miles upstream in the same time it

A sailboat can travel 60 miles, upstream in the same time it takes to travel 100 miles downstream. If the speed of the boast in still water is 20 miles per hour, what is the speed of the current?

60/(20-X)=100/(20+X)
100(20-X)=60(20+X)
2000-100X=1200+60X
-100X-60X=1200-2000
-160X=-800
X=-800/-160
X=5 MPH FOR THE CURRENT
PROOF
60/(20-5)=100/(20+5)
60/15=100/25
4=4