Chapter 8 - Polynomials and Factoring - 8-1 Adding and Subtracting Polynomials - Practice and Problem-Solving Exercises - Page 478: 43

The minus sign needs to be carried out to all three terms in the second set of parentheses.

The minus sign only attached to the first term $3x^2$, but not $-5x$ and $-6$. The $-5x$ and $-6$ become positive terms and the simplified answer should be: $x^2+4x+9$