Monochromatic light of wavelength 500 nm passes through two narrow slits separated by a distance d and forms an interference pattern on a screen 1.2 m away. The distance between adjacent bright fringes on the screen is measured to be 4.0 mm. What is the approximate value of the slit separation d?
a) 0.12mm
b) 0.15mm
c) 0.06mm
d) 0.30mm