(2x³ + x² − 4x) − (9x³ − 3x²)

To remove the parentheses:

1. If the parentheses has a + or nothing at all before
it, just erase the parentheses and the + if there is one
before it; otherwise just erase the parentheses.

2. If the parentheses has a - before it, change every sign
inside it and erase the parentheses and the - sign:

The first set of parentheses has nothing before it so 1
applies and we simply erase the parentheses and get:

  2x³ + x² − 4x − (9x³ − 3x²)

The remaining set of parentheses has a - before it so
we change the signs inside the parentheses and erase the
parentheses and the - sign before it:

  2x³ + x² − 4x − 9x³ + 3x²

Now we collect like terms:

The terms 2x³ and -9x³ combine to give -7x³.
The terms +x² and +3x² combine to give +4x².
So we end up with:

 -7x³ + 4x² - 4x   

Choice B

Edwin