a rectangle's area is simply width * length, so is the product of two factors.
in this case, we know that product, is 70x + 10, so, how can we tease out the factors from it?
well, our GCF from 70x and 10 is "10", but 10 itself is factorable into "2" and "5", so we can simply use that GCF and troupe to see what it might be.
