Answer:
40$
Explanation:
There are 60 minutes in an hour so if we break it down:
$10 = 15 minutes
$10 = 15 minutes
$10 = 15 minutes
$10 = 15 minutes
-------------------------
Add them together and we get:
$40 = 60 minutes or 1 hour
Meaning they would make 40$ in 1 hour.