(a-b)(4a-2b)=

$$\\(a-b)(4a-2b)\\\\ =a(4a-2b)\textcolor[rgb]{1,0,0}{-b}(4a-2b)\\\\ =4a^2-2ab-4ab--2b^2\\\\ =4a^2-2ab-4ab+2b^2\\\\ =4a^2-6ab+2b^2\\\\$$

nei (not enough information)