\(\frac{ hc }{3 \lambda}=\frac{ hc }{\lambda_{0}}+\frac{ e \cdot V }{4}\)\(...(ii)\)
(multiply by \(4\))
\(\frac{4 hc }{3 \lambda}=\frac{4 hc }{\lambda_{0}}+ eV\)\(...(iii)\)
From \((i)\) \(\&\) \((iii)\)
\(\frac{h c}{\lambda}-\frac{h c}{\lambda_{0}}=\frac{4 h c}{3 \lambda}-\frac{4 h c}{\lambda_{0}}\)
\(-\frac{ hc }{3 \lambda}=-\frac{3 hc }{\lambda_{0}}\)
\(9 \lambda=\lambda_{0}\)
\(n=9\)