For a transverse wave travelling along a straight line,

(2) Given : Distance between one crest and one trough

$=1.5 \mathrm{~m}$

$=\left(2 n_{1}+1\right) \frac{\lambda}{2}$

Distance between two crests $=5 \mathrm{~m}=n_{2} \lambda$

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

Here $n_{1}$ and $n_{2}$ are integer.

If $n_{1}=1, n_{2}=5 \quad \therefore \lambda=1$

$n_{1}=4, n_{2}=15 \quad \therefore \lambda=1 / 3$

$n_{1}=7, n_{2}=25 \quad \therefore \lambda=1 / 5$

Hence possible wavelengths $\frac{1}{1}, \frac{1}{3}, \frac{1}{5}$ metre.