Alright, let's work through 3991 times 2646 step by step
3991 × 2646 = 2646 × (3991)
+ 2646 × 1 yielding 2646
+ 2646 × 90 producing 238140
+ 2646 × 900 producing 2381400
+ 2646 × 3000 giving us 7938000

= 10560186
