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

Problem
Find the equation of a sphere of radius 3 and tangent to all three coordinate planes if the center is on the first octant.

A.   x2+y2+z29=0
B.   x2+y2+z26x6y6z+18=0
C.   x2+y2+z24x4y4z+12=0
D.   x2+y2+z28x8y8z+14=0