Can someone explain these two questions.. it gives the answer but I have to show how to get that answer.. even if you can just help with one it’d help!! Please

Acircle has a radius of 5/6 units and is centered at (3.6, 7.8) write the equation of this circle

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?

Given that abcd is a rhombus, what is the value of x?