Pls help me understand this.

Answer:
4 Square units
Step-by-step explanation:
The height is incorect
It is meant to be the vertical height which is the distance from A to AB (3 - 1 = 2)
[tex] \frac{1}{2} bh = \frac{1}{2} \times 4 \times 2 \\ = 4 \: square \: units[/tex]