Equation of the sphere of radius 3 and tangent to coordinate-planes

Center (h, k, l) is at C(3, 3, 3)
Radius, r = 3
 

$(x - h)^2 + (y - k)^2 + (z - l)^2 = r^2$

$(x - 3)^2 + (y - 3)^2 + (z - 3)^2 = 3^2$

$(x^2 - 6x + 9) + (y^2 - 6y + 9) + (z^2 - 6z + 9) = 9$

$x^2 + y^2 + z^2 - 6x - 6y - 6z + 18 = 0$   ←   answer