Need help with question 1 and 2 PLEASE

What properties allow transformation to be used as a problem solving tool

The total cost of anja’s trip to the dentist was $628.35. she paid a flat fee of $89.95 which included the checkup and cleaning and then had 4 cavities filled, each of which cost the same amount. which shows the correct equation and value of x, the cost of each cavity filling?

How can you find the mean absolute deviation (mad) for this set of data?