Answer
$7x; 9x^{2} - 4$
Work Step by Step
$63x^{3} - 28x$
We see that that two terms have a 7x common so we can factor it out of the two terms
$7x(9x^{2} - 4)$
Since the Area of a square is length x length, the length could be either 7x or $9x^{2} - 4$
