(a) Given, y=a sin (100$\ \pi$t-3x)
The general equation,
$k = 3\ and\ k = \frac{2\pi}{\lambda}$
Or
$\lambda = \frac{2\pi}{k}$
$\lambda = \frac{2\pi}{3}$
Phase difference, $\phi = \frac{\pi}{3}$
$\frac{2\pi}{\lambda}.x = \frac{\pi}{3}$
$or\ \ \ \ x = \frac{\pi}{3} \times \frac{\lambda}{2\pi}$
$x = \frac{\pi}{3} \times \frac{2\pi}{3 \times 2\pi}$
Distance,
$x = \frac{\pi}{9}m$