Alright, let's work through 6421 times 3078 step by step
6421 × 3078 = 3078 × (6421)
+ 3078 × 1 that is equal 3078
+ 3078 × 20 yielding 61560
+ 3078 × 400 which equals 1231200
+ 3078 × 6000 that is equal 18468000

= 19763838
