Only problem I need help on. Please help on B, thank you.

Iwill make brain if you me correctly fill this out needs due today pls and send it back to me (click the link and you will get it)

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?

What is the missing reason in the proof? segment addition congruent segments theorem transitive property of equality subtraction property of equality?