Alright, let's work through 3991 times 5464 step by step
3991 × 5464 = 5464 × (3991)
+ 5464 × 1 what gives us 5464
+ 5464 × 90 yielding 491760
+ 5464 × 900 yielding 4917600
+ 5464 × 3000 giving us 16392000

= 21806824
