Roger works part time as a waiter at a pizza joint. He earns $ 9 per hour how does he earn 20 hours of work

If Rodger is working 20hs and gets $9 per hour you would do this:

1 - $9 * 20 = $ 180 per hour

2 - check work = $ 180 / 9 = 20hs

3 - now that you know your answer is $180 you would say this: Rodger will earn a total of $180 if he works 20hs and gets payed $9 an hour