How to create a distributed equation out of this scenario?

[geol19]

I have to give a presentation on what kind of math a paralegal would have to use. My friend came up with this, but we can't figure out how to get the equation. If the distribution property is not the right one for this problem then can you please recommend the right one.
Now if I want wanted to find out how many hours a particular client was charged for I would have to put it into a problem. It is 300 dollars an hour for the services of my lawyer. Let’s say that I made a mistake with the book keeping book and did’t write down the appropriate numbers and messed it up. So I don’t know how many hours that the client was with us.