Alright, let's work through 6237 times 3420 step by step
6237 × 3420 = 3420 × (6237)
+ 3420 × 7 what gives us 23940
+ 3420 × 30 what gives us 102600
+ 3420 × 200 yielding 684000
+ 3420 × 6000 giving us 20520000

= 21330540
