Rubric, Inc. provided the following inventory transaction summary for May:

$5/1$ Purchased $200$ units @ $$3\mathrm{.}00$ per unit

$5/15$ Sold $40$ units

$5/21$ Purchased $300$ units @ $$5\mathrm{.}00$ per unit

$5/31$ Purchased $40$ units @ $$10\mathrm{.}00$ per unit

In addition, it has been determined that Rubric's inventory at the beginning of the month was $$400\mathrm{.}00(200$ units$).$ What was Rubric's cost per unit at the end of May, using the moving average method?

$$2\mathrm{.}00$

$$4\mathrm{.}00$

$$3\mathrm{.}00$

$$6\mathrm{.}00$