If a plumber earns 22 dollars per job. Then he goes to 3 jobs but in addition he gets paid 38 dollars an hour. If with those 3 jobs he earned more than 350 dollars. Do you know how many hours the plumber worked?
The problem only tells you that he earned more than 350 dollars. So it could be much, much higher, or it not be. If it told us a precise amount of money, we would be able to find out how many hours he worked.
