What is the magnitude of potential energy at infinity distance?

$A$ particle of mass $m$ is placed at the centre of a uniform spherical shell of mass $3m$ and radius $R$. The gravitational potential on the surface of the shell is

The $S.I.$ unit of gravitational potential is

Define gravitational potential. Give its unit. Is gravitational potential a vector or a scalar quantity?

The masses $m$ in figures $(A)$ and $(B)$ are identical. The gravitational potential energy in the two cases are $U_A$ and $U_B$. Then

$A$ particle of mass $10\, g$ is kept on the surface of a uniform sphere of mass $100\, kg$ and radius $10\, cm$. Find the work to be done against the gravitational force between them to take the particle far away from the sphere (you may take $G = 6.67 \times 10^{-11}\, Nm^2 / kg^2$).