Explanation

(b) From relation
$\mathrm{\Delta}\phi = \frac{2\pi}{\lambda} \times \mathrm{\Delta}x$
$\Longrightarrow \mathrm{\Delta}x = \frac{\lambda}{2\pi} \times \mathrm{\Delta}\phi\ \ \ldots(i)$
$also,\ \ \ \ \ \ \lambda = \frac{v}{n}\ \ \ \ \ \ \ \ \ldots(ii)$
now, from Eqs.(i)and (ii), we get
$\mathrm{\Delta}x = \frac{v}{2\pi n} \times \mathrm{\Delta}\phi$
$\Longrightarrow \ \ \ \mathrm{\Delta}x = \frac{330}{2\pi \times 50} \times \frac{\pi}{3}$
Or $\mathrm{\Delta}x$=1.1m