Answer
a) $27.1\;\rm V$
b) $-4.34\times 10^{-18}\;\rm J$
Work Step by Step
$$\color{blue}{\bf [a]}$$
The proton is assumed to be a point charge, so its electric potential at the electron's position is given by
$$V=\dfrac{1}{4\pi \epsilon}\dfrac{q_e}{r}\tag 1$$
Plug the known;
$$V=(8.99\times 10^9)\dfrac{1.6\times 10^{-19}}{0.053\times 10^{-9}}$$
$$V=\color{red}{\bf 27.1}\;\rm V$$
$$\color{blue}{\bf [b]}$$
The electric potential energy of the electron is then given by
$$U_e=(-q_e)V$$
Plug from (1),
$$U_e=\dfrac{1}{4\pi \epsilon}\dfrac{-q_e^2}{r} $$
Plug the known;
$$U_e=(8.99\times 10^9)\dfrac{-(1.6\times 10^{-19})^2}{0.053\times 10^{-9}}$$
$$U_e=\color{red}{\bf -4.34\times 10^{-18}}\;\rm J$$
