He earned 32 for 4 hours, so you have 32/4.
Then you want to find the number of hours to make 80, so you have 80/h.
Set them to equal each other:
32/4 = 80/h
Now cross multiply:
(32 * h) / (4 *80)
Simplify:
32h = 320
Divide both sides by 32:
h = 320 / 32
h = 10
He will need to work 10 hours.
