For the travelling harmonic wave

y (x, t) = 2.0 cos 2$\pi $ [10t - 0.0080x + 0.35] where x and y are in cm and t in s. Calculate the phase difference between oscillatory motion of two points separated by a distance of (a) 4 cm, (b) 0.5 m, © $\lambda $/2 (d) 3$\lambda $/4.