–2n(5 + n – 8 – 3n)

Multiply each element by the factor outside.

-2n*5 + -2n*n - -2n*8 - -2n*3n

Simplify it

-10n + -2n² - -16n - -6n²

-10n + -2n² + 16n + 6n²

6n + 4n²

Radix's simplifying before the multiplication is a good idea. Best to keep things simple if possible.

-2n*(5+n-8-3n) = -2n*(-3-2n) = 6n+4n²