\(C = \frac{{k{\varepsilon _0}(l \times b)}}{d}\,\,\, \Rightarrow \,2 \times {10^{ - 6}} = \frac{{2.5 \times 8.85 \times {{10}^{ - 12}}(l \times 400 \times {{10}^{ - 3}})}}{{0.15 \times {{10}^{ - 3}}}}\,\,\, \)
\(\Rightarrow \,\,l\,\, = \,\,33.9\,\,m\)