I would do 120 - 45. Now that she has 75 left I would do 75 - 15 * 3 Since 45 Is all that she has left.
If I were you choose a variable I would say h for hours. And h is equal to 3.
In result the whole equation would be 120 - 45 - 15 * h but since h is equal to 3 , We can write it as 120 - 45 - 15 * 3. Leaving Audrey with $30 left.
Correct me if I am wrong :)