Answer
$2.33\mu m$
Work Step by Step
We can see that the slope of the graph is $12/1$. From equation (36-6), we know that the slope should be equal to $\pi a /\lambda$. Now we can use the given wavelength to solve for the slit width of the diffraction pattern, a.
$12=\pi a /\lambda$
$a = 12 \lambda/\pi$
$a = 12*610*10^{-9}m/\pi$
$a = 2.33*10^{-6}m$
$a = 2.33\mu m$
