Question 191391
Let x represent the distance between the starting point and the falls.

The time spent on the way to the falls is x/3.
The time spent on the way from the falls is x/5.
As the total time spent is 7.5 hours, we have
{{{x/3+x/5 = 7.5}}}
Solving for x, we have
{{{5x + 3x = 112.5}}} multiply both sides by 3x5.
{{{8x = 112.5}}}
x = 14.0625 km