Answer
$2n^{5}+n^{4}-n^{3}+n^{2}-n+3$
Work Step by Step
$ \begin{array}{ccccccccc}
& & n^{4} & -n^{3} & +n^{2} & -n & +1 & & (*)\\
& & & & & 2n & +3 & & \\
& & -- & -- & -- & -- & -- & & \\
& & 3n^{4} & -3n^{3} & +3n^{2} & -3n & +3 & ... & \leftarrow 3\times(*)\\
& 2n^{5} & -2n^{4} & +2n^{3} & -2n^{2} & +2n & & ... & \leftarrow 2n\times(*)\\
\hline & & & & & & & & \\
& 2n^{5} & +n^{4} & -n^{3} & +n^{2} & -n & +3 & ... & \leftarrow combine
\end{array}$