Answer
$2b(10x+7)(2x-5)$
Work Step by Step
For the polynomial
$$
40bx^2 -72bx -70b=2b(20x^2-36x-35)
$$
we check the factors of $ac=20(-35)=-170$. The only factors that can give the right middle term are $-50$ and $14$, as follows
$$
40bx^2 -72bx -70b=2b(10x+7)(2x-5)
.$$
