PLEASE I WILL GIVE EXTRA POINTS AND BRAINLIEST I PROMIS

What is the missing reason in step 5? linear pair postulategivendefinition of complementary anglescongruent complements theorem

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?

2x minus y equals 6, x plus y equals negative 3