Alright, let's work through 8004 times 6400 step by step
8004 × 6400 = 6400 × (8004)
+ 6400 × 4 that equals 25600
+ 6400 × 00 what gives us 0
+ 6400 × 000 yielding 0
+ 6400 × 8000 giving us 51200000

= 51225600
