# THIS EXURSION WITH A BOAT TRAVEL 35KM UPSTREAM AND THEN BACK AGAIN IN 4 H 48 MINUTRE. iF THE SPEED OF THE BOAT I5 K,/H, WHAT IS THE SPEED OF THE CURRENT?

Let v be the speed of the current. The boat's speed upstream (relative to the land) is 15-v and the speed downstream is 15+v. The total trip time is

35/(15-v) + 35/(15 + v) = 4.8 (hours)

Solve for the single unknown, v.