Explanation

(a) Velocity of wave (v)=360 m/s
Frequency, n= 600Hz
Phase difference, $\mathrm{\Delta}\Phi = 60ο$
If the minimum distance between two points is ∆x, then
$\mathrm{\Delta}x = \frac{\lambda}{2\pi} \times \mathrm{\Delta}\Phi$
$\Delta x = \frac{v}{2\pi n} \times \mathrm{\Delta}\Phi$
Or
$\mathrm{\Delta}x = \frac{360}{2\pi \times 600} \times 60$
$\mathrm{\Delta}x = \frac{360}{2\pi \times 600} \times \frac{\pi}{3}$
$\mathrm{\Delta}x = \frac{1}{10}m$
$\mathrm{\Delta}x = 10\ cm$