Question 380091
This is essentially a distribution problem.

Take the very first term, {{{8*n^2}}}, and distribute it into the second polynomial:
{{{8*n^2}}}*{{{ 3*n^2}}} + {{{8*n^2}}}*{{{-4*n}}} + {{{8*n^2}}}*{{{5}}}
Remember: when multiplying monomials, multiply coefficients and add exponents.
{{{24*n^4 - 32*n^3 + 40*n^2}}}

Then take the other term in the first parentheses, {{{-1}}}, and distribute it into the second polynomial:
{{{-1}}}*{{{3*n^2}}} + {{{-1}}}*{{{-4*n}}} + {{{-1*5}}}
{{{-3*n^2+4*n-5}}}

Put all of it together, then combine like terms:
{{{24*n^4 - 32*n^3 + 40*n^2}}}+{{{-3*n^2+4*n-5}}}
{{{24*n^4-32*n^3+37*n^2+4*n-5}}}