\[5n^{2}(3n + 1) - 2n\left( 5n^{2} - 3 \right) =\]
\[= 15n^{3} + 5n^{2} - 10n^{3} + 6n =\]
\[= 5n^{3} + 5n^{2} + 6n.\ \]