Answer: -10
Explanation:
Look at the number line. The "greater" the negative value is, i.e. -9 and -3, the farther to the left it is on the number line. On the other hand, -3 is farther to the right of the number line and is therefore larger than -9.
You can apply this same concept to your question. Since -10,000, -1,000, and -100 will be farther to the left of the number line than -100, you can find that -10 is the greatest number.