Alright, let's work through 6439 times 620 step by step
6439 × 620 = 620 × (6439)
+ 620 × 9 that results in 5580
+ 620 × 30 producing 18600
+ 620 × 400 yielding 248000
+ 620 × 6000 yielding 3720000

= 3992180
