Alright, let's work through 6443 times 3137 step by step
6443 × 3137 = 3137 × (6443)
+ 3137 × 3 that results in 9411
+ 3137 × 40 that results in 125480
+ 3137 × 400 giving us 1254800
+ 3137 × 6000 that results in 18822000

= 20211691
