b
\({C_1}\,\, = \,\,20\,\mu F\,\, = \,\,\frac{{{ \in _0}A}}{d},\,\,\,\,\,{C_2}\,\,\frac{{{ \in _0}A}}{{\left[ {d\,\, - \,\,t\,\, + \;\,\frac{t}{{{ \in _r}}}} \right]}}\)

\(\frac{{{C_1}}}{{{C_2}}}\,\, = \,\,\left[ {\frac{{d\, - \,\,t\,\, + \;\,\frac{t}{{{ \in _r}}}}}{d}} \right]\,\, \Rightarrow \,\,{C_2}\,\, = \,\,{C_1}\,\,\left[ {\frac{{d\,\, - \,\,t\,\, + \;\,\frac{t}{{{ \in _r}}}}}{d}} \right]\)