Let's say that you work for h hours. Then since each hour, you charge $10.25, then your total earnings after h hours will be:
10.25 + 10.25 + 10.25 + ... + 10.25, where you add 10.25 to itself h times.
Adding a number n to itself x times is the same as multiplying that number n by x: nx. It's the same thing here: we multiply 10.25 by h because we added 10.25 to itself h times:
10.25 * h
Now, we do know that the actual total amount of money you earn is $8425, so we can just set this value equal to our above expression: