Answer:
-9
Explanation:
The problem can be easily solved if you know your cube table. Because by knowing that, you know that 9³ is 729, meaning that -9³ would be -729.
Without knowing your cube tables, you can do -9 x -9 x -9 = -729.
Since -9 x -9 = 81, you can use a calcuator or solve on paper for 81 x -729.