Answer
(w-10z)(w-4z)
Work Step by Step
You are given $w^{2}$-14wz+40$z^{2}$. Factor it out:
$w^{2}$-10wz-4wz+40$z^{2}$ -break out the middle value-
($w^{2}$-10wz)+(-wz+40$z^{2}$) -group the first two and last two terms-
w(w-10z)-4z(w-10z) -Find the GCF of each grouping's-
(w-4z)(w-10z) -factor out the common term-
=(w-4z)(w-10z)