(b) $V_{P} = \frac{1}{4\pi\varepsilon_{0}}\left\lbrack \frac{q_{1}}{0.2} + \frac{q_{2}}{0.2} + \frac{q_{3}}{0.3} \right\rbrack$
$= 9 \times 10^{9}\left\lbrack \frac{1}{0.2} - \frac{2}{0.2} + \frac{3}{0.3} \right\rbrack \times 10^{- 6}$
$= 9 \times 10^{3}\lbrack 5 - 10 + 10\rbrack = 45 \times 10^{3} = 45kV$