Question

5.) A boat makes a trip downstream in 5 hours. The return trip against the current takes 12 hours. If the speed of the current is 3 1/2 km/h, what is the speed of the boat in still water?

6.) How far does the boat referred to in Exercise 5 travel (one-way)?

Answer 1

The boat travels downstream at the rate of r+3.5 and r-3.5 upstream.
distance down stream = r*time = (r+3.5)*5 and upstream is (r-3.5)*12.
Since the distance downstream is the same as distance upstream, these two are equal to each other.
(r+3.5)*5 = (r-3.5)*12
Solve for rate of the boat in still water.
That should help you solve b part.