Three concentric matallic shells A , B and C of radii R , 2R and 3R have surface charge densities $\;\sigma , -\sigma\;and\;\sigma\;$ respectively . Find the potential difference between A & C

Question

$(a)\;\large\frac{\sigma\;R}{\in_{0}}\qquad(b)\;\large\frac{2\;\sigma\;R}{\in_{0}}\qquad(c)\;zero\qquad(d)\;\large\frac{4\;\sigma\;R}{\in_{0}}$