Blue Book Test 4 Section 9 Math Question

<p>Hi. I don't understand how to get to this answer. Please advise. Thanks.</p>

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<li> In the figure below, ABCD is a rectangle with BC=4 and AB=6. Points D, Q and R are different points on a line (not shown) that is parallel to AD. Points D and Q are symmetrical about line AB and points Q and R are symmetric about line CD. What is the length of PR?</li>
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