Answer
$L = 1.3~m$
Work Step by Step
From the graph, we can see that the fringe spacing is $\Delta y = \frac{1~cm}{3} = 0.33~cm$
We can find the distance to the screen:
$\Delta y = \frac{\lambda~L}{d}$
$L = \frac{\Delta y~d}{\lambda}$
$L = \frac{(0.33\times 10^{-2}~m)(0.25\times 10^{-3}~m)}{630\times 10^{-9}~m}$
$L = 1.3~m$
