Just add all the numbers together, the divide by the amount of numbers
First you do 4500 × 0.04
Then take that number and add it to 4500
Sixth grade
Because if you divide their total profit by the total amount of hours they worked, you would find that the sixth grade's income per hour is the highest.
Sixth grade: 170÷5=34
Seven grade: 112÷4=28
Eighth grade: 192÷6=32