$y=0.2 \sin 0.8 x \cos 3000 t$
The distance between any two points of minimum or maximum displacement is simply wavelength $\left(\frac{\lambda}{4}\right)$ of the wave.
$k=\frac{2 \pi}{\lambda}=0.8$
$\text { or } \lambda=\frac{2 \pi}{0.8}$
$\therefore \lambda=\frac{5 \pi}{2} m \Rightarrow \frac{\lambda}{4}=\frac{5 \pi}{8} \,m$
Hence answer must be $(d)$.
Statement$-2:$ Intensity of waves of given frequency in same medium is proportional to square of amplitude only.