The equation of sound wave is given by $\mathrm{y}=2\sin (314\mathrm{t}-4\mathrm{x}+\mathrm{\pi }/2)$ the wavelength of the wave is:

Given, $\mathrm{y}=2\sin (314\mathrm{t}-4\mathrm{x}+\mathrm{\pi }/2)$
The equation of progressive wave is given by
$\Rightarrow \mathrm{Y}=\mathrm{Asin}(\mathrm{KX}-\mathrm{\omega t})$

Comparing the given equation to the above equation
=> K = 4
Also, 

$\mathrm{K}=\frac{2\mathrm{\pi }}{\mathrm{\lambda }}$

then,
$\mathrm{\lambda }=\frac{2\mathrm{\pi }}{4}=\frac{\mathrm{\pi }}{2}=\mathbf{1}\mathbf{.}\mathbf{57}\mathbf{ }\mathbf{m}$.