(5x-10y)(3x-7y)
(10y-5x)(7y-3x)
(10y-5x)(3x-7y)
5(2y-x)(7y-3x)
\[(5x - 10y)(3x - 7y) =\]
\[= (10y - 5x)(7y - 3x) =\]
\[= 5 \cdot (2y - x)(7y - 3x).\]