\(C\) to \(C\, 5 m\)

\(T\) to \(C =\left(2 n _{1}+1\right) \frac{\lambda}{2}\)

\(C\) to \(C = n _{2} \lambda\)

\(\frac{1.5}{5}=\frac{\left(2 n _{1}+1\right)}{2 n _{2}} \Rightarrow 3 n _{2}=10 n _{1}+5\)

\(n _{1}=1, n _{2}=5 \rightarrow \lambda=1\)

\(n _{1}=4, n _{2}=15 \rightarrow \lambda=1 / 3\)

\(n _{1}=7, n _{2}=25 \rightarrow \lambda=1 / 5\)