Explanation:
999 × 109 = 999000000000, 999 → 9,990 → 99,900 → 999,000 → 9,990,000 → 99,900,000 → 999,000,000 → 9,990,000,000 → 99,900,000,000 → 999,000,000,000. Nine hundred ninety-nine billion in numbers, generally speaking, is 999000000000. In figures, 999000000000 is written with thousand separators as 999,000,000,000.