<p><a href="http://i.imgur.com/2UBpUqi.png%5B/url%5D">http://i.imgur.com/2UBpUqi.png</a></p>
<p>The key is finding the length of AB how do you do that? Answer is C, 105</p>
<p>Simple. Draw a line perpendicular to CD. You can then find AB by using the pythagorean theorem</p>
<p>I meant perpendicular to AD</p>
<p>That’s what I did, but you only have 17 for one of the legs. You still need the hypotenuse to find out the other leg.</p>
<p>Good, you’ve decided you need AB. Look at the entire shape. When you draw a line perpendicular to AD from point B, what two smaller shapes do you make? What do you know about those two shapes, including the side lengths of the smaller shapes? How could you use those new side lengths to find AB? (Think about your previous problem and how to use the given information!)</p>
<p>(You actually don’t need AB. When you divide the quadrilateral into two smaller shapes, you are given a lot of information that could potentially give you area.)</p>
<p>Well, I got that a line perpendicular to AD from point B would make a right triangle and a rectangle. Since one side of the rectangle is 17, one leg of the right triangle would be 17. But, what now? The area of the new rectangle formed is 91, and you need to add that to the area of the right triangle. </p>
<p>I figure that finding out AB would the quickest way to do it instead of dividing it up into smaller shapes and getting confused/messing up and whatnot.</p>
<p>Good, you’ve figured out the area of the rectangle, and now all you need is the area of the triangle.</p>
<p>To find the area of a triangle, you need two things, like you said correctly: both legs. You know one, but how would you get the length of the lower leg? Note that you know two things: first, you know that AD is 17. BC is 13, which is shorter than AD. AD and BC are parallel. Think about the relationship between that shorter, lower leg, BC, and AD. (BC+what=AD?)</p>
<p>Yes, you could definitely use AB. However, I never memorized the formula for the area of a trapezoid-- but if you’ve got it, more power to you, and definitely use it. (In that case, in order to get AB, the only way I can see would be finding both legs of the smaller triangle, for which, see above.)</p>
<p>Sorry, I still don’t get it, lol. I’m definitely overlooking some basic Math principle/idea here (never paid attention in math class)</p>
<p>Take it as a trapezoid. Area = (base1+base2)x height /2 you have both bases and CD is that height as it’s perpendicular to both</p>
<p>Nevermind… I failed to read the question properly and disregarded that CD = 7</p>