The problem asks to factor out the greatest common factor from the expression $9z(c-7z) + 4(-7z+c)$. The hint suggests checking if the expressions in the parentheses are equal.

1. Problem Description

The problem asks to factor out the greatest common factor from the expression $9z(c-7z) + 4(-7z+c)$. The hint suggests checking if the expressions in the parentheses are equal.

2. Solution Steps

First, observe that the expressions in the parentheses are the same: $(c-7z)$ and $(-7z+c)$. We can rewrite the expression as $9z(c-7z) + 4(c-7z)$.

Now we can factor out the common term $(c-7z)$ from both terms:

$9z(c-7z) + 4(c-7z) = (9z + 4)(c-7z)$.

3. Final Answer

$(9z+4)(c-7z)$