the goal is to get the equation in the following form ...

where (h,k) are the center coordinates and r is the radius.

start by dividing every term by 4 ...

group the x-vales and y-values together, move the constant ...

you now want to complete the square for both x and y ... half the coefficient of each linear term, square the result, and add to both sides of the equation ...

factor the quadratic trinomials of x and y ...

now, do you "see" h, k, and r?