Coherent green light of wavelength \(530 \mathrm{~nm}\) passes through two narrow slits for which the center-to-center separation distance is \(100 \mu \mathrm{m}\). What is the difference in phase between the waves from the two slits for those that arrive at a distant screen at an angular position \(\theta\) of

(a) \(15.4^{\circ}\) and \(

(b) 20. 7^{\circ}\) ?