Find the area of a closed figure ABCO, where $$A(0, 3)$$, $$B(4, 3)$$, $$C(4, 0)$$ and O is the origin.

A

$$6\ \text{unit}^2$$

B

$$24\ \text{unit}^2$$

C

$$18\ \text{unit}^2$$

D

$$12\ \text{unit}^2$$