Answer
Lewis Acid: $FeBr_3$
Lewis Base: $Br^-$
Work Step by Step
$Br^-$ has a pair of electrons free, so, when it reacts with $FeBr_3$, it will give that pair to the $Fe$ atom.
Since $Br^-$ donates the pair of electrons, it is the Lewis base.
Since $FeBr_3$ receives that pair, it is the Lewis acid.
