The given equation of SHM wave is
$y=0.03\mathrm{s}\mathrm{i}\mathrm{n}\pi \left(2t-0.01x\right)m$
= $0.03\sin \left(2\pi t-0.01\pi x\right)m$
Comparing it with general equation, we get
$y=\mathrm{asin}\left(\omega t-kx\right)$
Where, $k=\frac{2\pi }{\lambda }\Rightarrow \lambda =200m$
The phase difference between two particles is given by
$\Delta \varphi =kx=\frac{2\pi }{\lambda }\times x$ … (i)
Here, x = 25 m
Substituting the values of x an $\lambda$ in Eq. (i), we get
$\Delta \varphi =\frac{2\pi }{200}\times 25=\frac{\pi }{4}rad$