A solid conducting sphere has net positive charge and radius $R=0\mathrm{.}800m.$ At a point $1\mathrm{.}20$ m from the center of the sphere, the electric potential due to the charge on the sphere is $21\mathrm{.}0$ V $.$ Assume that $V=0$ at an infinite distance from the sphere.

What is the electric potential at the center of the sphere?

Express your answer with the appropriate units.