Alright, let's work through 6440 times 3924 step by step
6440 × 3924 = 3924 × (6440)
+ 3924 × 0 that equals 0
+ 3924 × 40 that results in 156960
+ 3924 × 400 that equals 1569600
+ 3924 × 6000 giving us 23544000

= 25270560
