Answer
$4x^3-3x^2+8x+7$
Work Step by Step
Removing the grouping symbols and then combining like terms, the given expression simplifies to
\begin{array}{l}\require{cancel}
(3x^3+2x^2+8x)+(x^3-5x^2+7)
\\\\=
3x^3+2x^2+8x+x^3-5x^2+7
\\\\=
(3x^3+x^3)+(2x^2-5x^2)+8x+7
\\\\=
4x^3-3x^2+8x+7
.\end{array}
