Answer:
=

Explanation:
Given that:
=(1 - 3n3 + 2n4) + (8n4 – 13 – 7)
By opening the brackets we get:
= 1-3n3 +2n4 +8n4 -13 -7
By adding like terms: Constants into constants and variables with same powers of x.....
= -20 - 3n3 +10n4
So by arranging the answer in decreasing order of powers of x:
=

I hope it will help you!