Evaluate: (3-6n^5-8n^4)-(-6n^4-3n-8n^5)

Expression: $\left( 3-6{n}^{5}-8{n}^{4} \right)-\left( -6{n}^{4}-3n-8{n}^{5} \right)$

Remove unnecessary parentheses

$3-6{n}^{5}-8{n}^{4}-\left( -6{n}^{4}-3n-8{n}^{5} \right)$

When there is a $-$ in front of an expression in parentheses, change the sign of each term of the expression and remove the parentheses

$3-6{n}^{5}-8{n}^{4}+6{n}^{4}+3n+8{n}^{5}$

Collect like terms

$3+2{n}^{5}-8{n}^{4}+6{n}^{4}+3n$

Collect like terms

$3+2{n}^{5}-2{n}^{4}+3n$

Use the commutative property to reorder the terms

$2{n}^{5}-2{n}^{4}+3n+3$