The rectangle is actually a square. In fact, we have that the side PQ is equal to 2 other sides of the rectangle (QR and SP), and this is possible only if all the 4 sides of the rectangle are equal: this means it is a square.
SQ is the diagonal of the square: [tex]SQ = 6 \sqrt{2} [/tex], but we know that in a square, the diagonal is equal to square root of 2 times the length of the side:
[tex]d = \sqrt{2} L [/tex]
where d is the diagonal and L the length of the side. Since in our square the length of the diagonal is [tex]d= 6 \sqrt{2} [/tex], the length of the side must be
[tex]L= \frac{d}{ \sqrt{2} } = \frac{6 \sqrt{2} }{ \sqrt{2} }=6 [/tex]
so, the correct answer is b) 6.
