Answer
$7z^2$
Work Step by Step
Find the greatest common factor. Find the prime factors of each term and multiply the factors that are common to all the terms.
$14z^4=\underline7\times2\times\underline z\times \underline z\times z\times z$
$42z^3=\underline7\times3\times2\times\underline z\times \underline z\times z$
$21z^2=\underline7\times3\times\underline z\times \underline z$
GCF $=7\times z\times z=7z^2$
