Let us assume rent for a child = $x per hour and
Rent for an adult = $ y per hour.
We are given number of children = 3.
Number of adults = 1.
Rent for 3 children at the rate $x per hour = 3*x = 3x.
Rent for 1 adult at the rate $y per hour = 1*y = y.
We are given number of hours of rafting trip = h hours.
Total cost of 3 children and 1 adult for h hours =h times (Cost of 3 children and 1 adult for each hour).
= h*(3x+y).
Therefore, h(3x+y) is the final expression for the total cost of h hours of rafting trip.
If you are given values of x, y or h, you can plug those values in this expression.
