Alright, let's work through 9991 times 8909 step by step
9991 × 8909 = 8909 × (9991)
+ 8909 × 1 yielding 8909
+ 8909 × 90 yielding 801810
+ 8909 × 900 that results in 8018100
+ 8909 × 9000 producing 80181000

= 89009819
