LIFO inventory consisted of $1128$ units at $76\mathrm{.}68$ per unit at the beginning of $2018.$ During the second quarter of $2018,$ Darby sold $3,924$ units at $$95\mathrm{.}50$ per unit. If the cost to purchase inventory during the second quarter was $$78\mathrm{.}34$ per unit, how many units should Alpine purchase if its objective is to maximize profit?