The speed of the current is 7 mph. The boat travels three times slower against the current than with the current. What is the speed of the boat in still water?

Let the speed of the boat be x

so going against the current the speed is x-7

going with the current the speed is x+7

let the distance be d

time = distance / speed

time to go against the current = d / (x-7)

time to go with the current = d / (x+7)

time going against the current is 3 times going with the current

d / (x-7) = 3d / (x+7) ⇒⇒⇒ divide by d

1 / (x-7) = 3 / (x+7)

x+7 = 3 (x-7)

x+7 = 3x - 21

2x = 28

x = 14

So, the speed of the boat in still water is = 14 mph