d
\(q _{ x }=\sigma 4 \pi a ^2\)

\(q _{ y }=-\sigma 4 \pi b ^2\)

\(q _{ z }=\sigma 4 \pi c ^2\)

Potential \(x =\) potential \(z\)

\(V _{ x }= V _{ z }\)

\(\frac{ q _{ x }}{4 \pi \varepsilon_0 a }+\frac{ q _{ y }}{4 \pi \varepsilon_0 b }+\frac{ q _{ z }}{4 \pi \varepsilon_0 c }=\frac{ q _{ x }}{4 \pi \varepsilon_0 c }+\frac{ q _{ y }}{4 \pi \varepsilon_0 c }+\frac{ q _{ z }}{4 \pi \varepsilon_0 c }\)

\(\frac{\sigma 4 \pi a ^2}{ a }-\frac{\sigma 4 \pi b ^2}{ b }+\frac{\sigma 4 \pi c ^2}{ c }=\frac{4 \pi \sigma\left[ a ^2- b ^2+ c ^2\right]}{ c }\)

\(c ( a - b + c )= a ^2- b ^2+ c ^2\)

\(c ( a - b )= a ^2- b ^2\)

\(c = a + b\)

\(c =5\,cm\)