For a transverse wave travelling along a straight line, the distance between two peaks(crests) is 5 m, while the distance between one crest and one trough is 1.5 m. The possible wavelengths (in m) of the waves are:

Given Distance between one crest and one tough =1.5m  $=(2n_1+1)\frac{\lambda }{2}$
 
Distance between two crests= $5m=n_2\lambda$
 $\frac{1.5}{5}=\frac{(2n_1+1)}{2n_2}\Rightarrow 3_{n_2}={10}_{n_1}+5$
Here $n_1\&n_2$  are integer.
If  $n_1=1,n_2=5\therefore \lambda =1$
 $$\begin{gathered} n_1=4,n_2=15\therefore \lambda =1/3 \\ {n}_1=7,n_2=25\therefore \lambda =1/5 \end{gathered}$$
 Hence possible wavelengths $\frac{1}{1},\frac{1}{3},\frac{1}{5}$  metre