24. \( \left(9 r^{2}+4 r-7\right)+\left(3 r^{2}-3 r\right) \)

To simplify the expression: \[ \left(9 r^{2} + 4 r - 7\right) + \left(3 r^{2} - 3 r\right) \] **Step 1: Remove the Parentheses** Since both parentheses are preceded by a plus sign, you can remove them directly: \[ 9 r^{2} + 4 r - 7 + 3 r^{2} - 3 r \] **Step 2: Combine Like Terms** - **Combine \( r^{2} \) terms:** \[ 9 r^{2} + 3 r^{2} = 12 r^{2} \] - **Combine \( r \) terms:** \[ 4 r - 3 r = 1 r \quad \text{or simply} \quad r \] - **Constant term:** \[ -7 \] **Step 3: Write the Simplified Expression** \[ 12 r^{2} + r - 7 \] **Final Answer:** \[ 12 r^{2} + r - 7 \]