1. **State the problem:** Simplify the expression $8 (4+5)$. 2. **Apply the order of operations:** First, solve the expression inside the parentheses. 3. Calculate $4+5=9$. 4. Now multiply $8$ by the result: $8 \times 9$. 5. Perform the multiplication: $8 \times 9=72$. 6. **Final answer:** The simplified value of $8 (4+5)$ is $72$.