Answer
$92$
Work Step by Step
We know that
$dsin\theta=(m-\frac{1}{2})\lambda$
We plug in the known values to obtain:
$dsin(0.31^{\circ})=(1-\frac{1}{2})\lambda$
This can be rearranged as:
$\frac{d}{\lambda}=\frac{0.5}{sin(0.31^{\circ})}$
$\frac{d}{\lambda}=92$