Answer
$m=5$ minimum. We will see a dark spot.
Work Step by Step
We are trying to determine what appears, on a distant viewing screen, at a point at which the top and bottom rays through the slit have a path length difference equal to $5\lambda$.
We use equation (36-3) for a single-slit experiment.
$\alpha \sin \theta = m \lambda $ where $m=1,2,3,....$ (minima)
$\alpha \sin \theta = 5 \lambda $
$m=5$ (minima).
We would see a dark spot ( a minimum ).
