Find out how much he makes per hour.
Ex. $320/40 hours = $8 per hour
Find out how many hours he must work to make $416.
Ex. $416/ $8 per hour = 52 hours
Find the difference between 52 hours and 40 hours (the problem asks how many more hours).
Ex. 52 hours - 40 hours = 12 hours
Answer: 12 more hours