Answer
$15.71\;m^{-1}$
Work Step by Step
The equation for one of the two waves be of the form: $y(x, t)=y_m\sin(kx+\omega t)$
The other wave has the same amplitude and wavelength and travel through each other.
From the given graph, wavelength of each wave is
$\lambda=40\;cm=0.4\;m$
Therefore,
or, $k=\frac{2\pi}{\lambda}$
or, $k=\frac{2\pi}{0.4}\;m^{-1}$
or, $\boxed{k=15.71\;m^{-1}}$
