Answer: 5.4n^5, the 3rd option.
Explanation:
The first step to solve this is to use the distributive property to change this equation into: 4n^5 + 3.5n^5 - 2.1n^5.
Then, you add 4n^5 + 3.5n^5 which is 7.5n^5.
The last step is to subtract 2.1n^5 from 7.5n^5 which is 5.4n^5.
Hope this helped!