Answer
3.1 cm
Work Step by Step
The spacing on the screen between bright fringes is addressed in Example 24-1.
For light shining through 2 slits separated by a distance d, the spacing between successive fringes on a screen a distance $\mathcal{l}$ away is $\Delta x = \frac{\lambda \mathcal{l}}{d}$.
$$\Delta x = \frac{(633\times10^{-9}m)(3.3m)}{0.068\times10^{-3}m}=0.031m$$
