The volume of a cone is $3 \pi x^3$ cubic units and its height is $x$ units.
Which expression represents the radius of the cone's base, in units?
A$3 x$
B$6 x$
C$3 \pi x^2$
D$9 \pi x^2$
Which expression represents the radius of the cone's base, in units?
A$3 x$
B$6 x$
C$3 \pi x^2$
D$9 \pi x^2$