Which is used to find the number of ways a given number of objects can be ordered?

Really need on these. i have no idea what to do

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 many grams the dog will eat in 3 days?