No problem, we've got 6440 and 8400 to multiply
6440 × 8400 = 8400 × (6440)
+ 8400 × 0 what gives us 0
+ 8400 × 40 what gives us 336000
+ 8400 × 400 giving us 3360000
+ 8400 × 6000 which equals 50400000

= 54096000
