Value of potential at a point due to a point charge is

Three charged concentric nonconducting shells are given as shown in figure. Find the potential at point $A$

Twenty seven drops of same size are charged at $220\, \mathrm{~V}$ each. They combine to form a bigger drop. Calculate the potential of the bigger drop. (In $\mathrm{~V}$)

Two identical positive charges are placed at $x =\, -a$ and $x = a$ . The correct variation of potential $V$ along the $x-$ axis is given by

Uniform electric field of magnitude $ 100$ $V/m$ in space is directed along the line $y$ $=$ $3$ $+$ $x$. Find .........$V$ the potential difference between point $A (3, 1)$ $ \&$ $ B$ $ (1, 3)$

As shown in the figure, charges $ + q$ and $ - q$ are placed at the vertices $B$ and $C$ of an isosceles triangle. The potential at the vertex $A$ is