Answer
$(z+3)(z-7)$.
Work Step by Step
The given polynomial is
$=z^2-4z-21$
Rewrite $-4z$ as $3z-7z$.
$=z^2+3z-7z-21$
Group the terms.
$=(z^2+3z)+(-7z-21)$
Factor each group.
$=z(z+3)-7(z+3)$
Factor out $(z+3)$.
$=(z+3)(z-7)$
Hence, the factor of the polynomial is $(z+3)(z-7)$.
