Alright, let's work through 6643 times 3131 step by step
6643 × 3131 = 3131 × (6643)
+ 3131 × 3 that equals 9393
+ 3131 × 40 that equals 125240
+ 3131 × 600 producing 1878600
+ 3131 × 6000 giving us 18786000

= 20799233
