A solid conducting sphere of $10-$cm radius has a net charge of $18$ nC$.$ If the potential at infinity is taken as zero, what is the potential at the center of the sphere?

a$.$

$2\mathrm{.}1$ V

b$.$

$16$ V

c$.$

$>1\mathrm{.}6104$ V

d$.$

$13$V

e$.$

$1\mathrm{.}6103$ V