4. (2x2 - 3x + 5) - (x2 + 4x - 6)

This is a subtraction problem. The rules are still "Remove parentheses and combine like terms," but now the second parentheses have a minus sign in front of them. Subtract means "change the sign and add", so we change the signs on all the terms inside the second parentheses

2x2 - 3x + 5 - x2 - 4x + 6

Now combine like terms.

2x2 -x2 - 3x - 4x + 5 + 6

x2 - 7x + 11