I'll get ya started....
The equation of a circle in the form (x-h)^2 + (y-k)^2 = r^2 will give you the center h, k
Get the equation to that form
x^2 + 3x + y^2 - 6y = 0 'complete the square' for x and y
(x+ 1.5)^2 + (y -3)^2 = 2.25 + 9
center = -1.5, 3 radius = sqrt 11.25
Can you keep going from here?