Manuela makes $21 in commissions over the first three hours that she worked selling magazines. How many dollars must she make during the fourth hour to average $8 an hour for the full four hours

Answer: Manuela must make $11 dollars during the fourth hour

Step-by-step explanation:

In order to calculate the amount of dollars for the fourth hour, you have to calculate the amount of dollars she needs to make in the full four hours:

The average is the amount of dollars earned in 4 hours between the 4 hours. Let A be the average and d be the amount of dollars

A = d/4

A = $8. Replacing A in the expression:

8=d/4

Multiplying by 4 each side:

d=32

Now, if she must make $32 in four hours to average $8 but she already earned $21 in three hours then in the last hour she must make:

$32 - $21 = $11