Potential at centre
V = \(\frac kr[10^{-8}-2\times10^{-8}+6\times10^{-8}-4\times10^{-8}]\)
= \(\frac{10^{-8}k}{2\times10^{-2}}\)[ 1 - 2 + 6 - 4]
v = \(\frac{k\times10^{-8}}{2\times10^{-2}}\)
v = \(\frac{9\times10^9\times10^{-8}}{2\times10^{-2}}\)
v = 4.5 x 103 v