The difference between 68 and 23 is 45. The company charging 23$ has to be 45$ more for the amount of hours. When you multiply 180 by .4 you get 72, and when you multiply 180 by .65 you get 117. The difference is 45.
Sorry that I didn't show my work, I don't really know how to do this other than plugging in random numbers and 180 fits so...
