Alright, let's work through 6440 times 3404 step by step
6440 × 3404 = 3404 × (6440)
+ 3404 × 0 which equals 0
+ 3404 × 40 resulting in 136160
+ 3404 × 400 giving us 1361600
+ 3404 × 6000 that is equal 20424000

= 21921760
