4. (2*x*^{2} - 3*x* + 5) - (*x*^{2} + 4*x* - 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

2*x*^{2} - 3*x* + 5 - *x*^{2} - 4*x* + 6

Now combine like terms.

2*x*^{2} -*x*^{2} - 3*x* - 4*x* + 5 + 6

*x*^{2} - 7*x* + 11