A simple harmonic progressive wave is represented by the equation : $y=8\mathrm{sin}2\pi \left(0.1x-2t\right)$ where x and y are in cm and t is in seconds. At any instant the phase difference between two particles separated by 2.0 cm in the x-direction is

(1) 18°

(2) 36°

(3) 54°

(4) 72°