Monochromatic Laser Light of Frequency 5

Monochromatic laser light of frequency 5.20 × 10¹⁴ Hz is shown on a pair of thin parallel slits,and the pattern is viewed on a screen 1.20 m away.The fifth bright fringes (not counting the central fringe)occur at ±2.12 cm on either side of the central bright fringe.The entire apparatus is now immersed in a transparent liquid.When the experiment is repeated,the fifth bright fringes now occur at ±1.43 cm from the central bright fringe.(c = 3.00 × 10⁸ m/s)
(a)How far apart are the slits?
(b)What is the index of refraction of the liquid?