Two narrow, parallel slits separated by 0.250 mm are illuminated by green light (& # 546.1 nm).

Question:

Two narrow, parallel slits separated by 0.250 mm are illuminated by green light (& # 546.1 nm). The interference pattern is observed on a screen 1.20 m away from the plane of the slits. Calculate the distance
(a) From the central maximum to the first bright region on either side of the central maximum and
(b) Between the first and second dark bands.