SAT 1 Math problem?

Test Preparation SAT Preparation
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<p><a href="http://i.imgur.com/Nm0nb.png%5B/url%5D"&gt;http://i.imgur.com/Nm0nb.png&lt;/a&gt;&lt;/p>

<p>What I do is find the area of ABC, which would be 36. Then subtract the area of BCD from it which is 12. I get 24 as the answer, but it isn't one of the choices. I don't know what i'm doing wrong and would appreciate it if someone could help me find my mistake. Thanks!
If anyone was wondering this is problem 18.</p>

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<p>No, the area of a triangle is (1/2)BH. So the area of ABC is 18, and the area of BCD is 6. The answer is 18 - 6 = 12, which is answer C.</p>

3

<p>WOW I feel like a total idiot, alright thanks very much.</p>