Physics i don't understand, help!

Question

Monochromatic light with a wavelength of 6.4 E -7 meter passes through two narrow slits, producing an interference pattern on a screen 4.0 meters away. The first order bright band lines are 2.0 E -2 meters away from the central bright maxima.

What is the distance between the slits?

Answer 1

The position of bright fringes is given by:

γ = L (mλ / d)

Solve for the distance between the slits.

d = (mλ) / (γ / L)

= (1 x (6.4 x 10^-7 m)) / ((2.0 x 10^-2 m) / 4.0 m)

= 1.28 x 10^-4 m