Alright, let's work through 6688 times 1557 step by step
6688 × 1557 = 1557 × (6688)
+ 1557 × 8 that is equal 12456
+ 1557 × 80 that equals 124560
+ 1557 × 600 which equals 934200
+ 1557 × 6000 producing 9342000

= 10413216
