No problem, we've got 8437 and 644 to multiply
8437 × 644 = 644 × (8437)
+ 644 × 7 that equals 4508
+ 644 × 30 that is equal 19320
+ 644 × 400 resulting in 257600
+ 644 × 8000 which equals 5152000

= 5433428
