For brainiest and 50 points a ferry can travel 100 miles with the current in the same amount of time it takes to travel 60 miles against the current. if the speed of the ferry is 40 mph, what is the speed of the current?

X - speed of the current
40+x - speed with current 
40-x - speed against current

t-time
(40+x)*t=100
(40-x)*t=60

           40t+xt=100
   +      40t-xt = 60
           80t      =160
                t      = 2

40t+xt=100,   
40*2+2x=100
80+2x=100
2x=100-80
2x=20
x=10 mi/h

10 mi/h speed of the current.