<p>Because you want the height of the parallelogram, and not just multiplying the sides. The twelve comes in simply because (I hope you can see what I’m trying to explain) you need the height of the parallelogram, and if you look at the picture of the diagram in your SAT book, can you kind of see how “dragging” the twelve side to the middle of the parallelogram give you the height? </p>
<p>[Area</a> of a Parallelogram](<a href=“http://www.mathgoodies.com/lessons/vol1/area_parallelogram.html]Area”>http://www.mathgoodies.com/lessons/vol1/area_parallelogram.html)</p>
<p>Check this website out, or at least the red pictures with the height labeled. Now if you put your triangle next to it, the twelve side will be the height. </p>
<p>Can you see that? I hope I explained it properly.</p>