Alright, let's work through 6399 times 1988 step by step
6399 × 1988 = 1988 × (6399)
+ 1988 × 9 which equals 17892
+ 1988 × 90 giving us 178920
+ 1988 × 300 producing 596400
+ 1988 × 6000 yielding 11928000

= 12721212
