Answer
$10z^{4}-26z^{3}+20z^{2}-22z+12$
Work Step by Step
$ \begin{array}{lllllll}
& & & 5z^{3} & -3z^{2} & +4z & -3\\
& & & & & 2z & -4\\
& & & & -- & -- & --\\
& & & -20z^{3} & +12z^{2} & -16z & +12\\
& & 10z^{4} & -6z^{3} & +8z^{2} & -6z & \\
\hline & & & & & & \\
& & 10z^{4} & -26z^{3} & +20z^{2} & -22z & +12
\end{array} \qquad \begin{array}{l}
.\\
.\\
.\\
\leftarrow-4(5z^{3}-3z^{2}+4z-3)\\
\leftarrow 2z(5z^{3}-3z^{2}+4z-3)\\
\\
\leftarrow\text{combine }
\end{array}$