A problem states that Ursula earns $9 per hour. To write an expression that tells how much money Ursula earns for h hours, Joshua wrote 9 divided by h. Sarah wrote 9h. Whose expression is correct and why?

The correct one would by 9h because you are asking how much will Ursula make per hour. So let's say that h is 10, then in order to know how much Ursula makes per hour, you have to add 9 ten times. A short way to do that would be to simply multiply 9 with 10 so that you can get the answer of 90. It cannot be 9/h because then answer will be much lower than it is supposed to be. So the answer to the question is really 9h.