If you would like to simplify the difference (–7x – 5x^4 + 5) – (–7x^4 – 5 – 9x), you can do this using the following steps:
(–7x – 5x^4 + 5) – (–7x^4 – 5 – 9x) = -7x - 5x^4 + 5 + 7x^4 + 5 + 9x = 2x^4 + 2x + 10
The correct result would be a. 2x^4 + 2x + 10.
