Answer
$21x^{5}-43x^{4}+38x^{3}-24x^{2}$
Work Step by Step
$ \begin{array}{lllllll}
& & & & 7x^{3} & -5x^{2} & +6x\\
& & & & & 3x^{2} & -4x\\
& & & & -- & -- & --\\
& & & & -28x^{4} & +20x^{3} & -24x^{2}\\
& & & 21x^{5} & -15x^{4} & +18x^{3} & \\
\hline & & & & & & \\
& & & 21x^{5} & -43x^{4} & +38x^{3} & -24x^{2}
\end{array} \qquad \begin{array}{l}
.\\
.\\
.\\
\leftarrow-4x(7x^{3}-5x^{2}+6x)\\
\leftarrow 3x^{2}(7x^{3}-5x^{2}+6x)\\
\\
\leftarrow\text{combine }
\end{array}$
