Hello there!
[tex](3 - 6n^5-8n^4)-(6n^4-3n-8n^5)[/tex]
Start by distributing the negative sign
[tex]3 - 6n^5-8n^4-6n^4+3n+8n^5[/tex]
Combine like terms
[tex]-6n^5 + 8n^5 - 8n^4-6n^4+3n + 3[/tex]
[tex]=2n^5 - 14n^4+3n+3[/tex]
Let me know if you have any questions about the answer. As always, it is my pleasure to help students like you!