this math question stumped me

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1

<p><a href="http://img8.imageshack.us/img8/6804/picture1b.png%5B/url%5D"&gt;http://img8.imageshack.us/img8/6804/picture1b.png&lt;/a&gt;&lt;/p>

<p>The figure shows three squares with sides of length 5, 7, and x, respectively. If A, B, and C lie on line l, what is the value of x?</p>

<p>Ty for helping</p>

2

<p>The slopes between each two points must be equal.</p>

<p>Thus,</p>

<p>2 / 5 = (x - 7) / 7</p>

3

<p>Think slope (rise/run) and how you can use that to find the 3rd point and then finally the size of the last square.</p>