Let's calculate 8991 x 1991
8991 × 1991 = 1991 × (8991)
+ 1991 × 1 that results in 1991
+ 1991 × 90 what gives us 179190
+ 1991 × 900 that results in 1791900
+ 1991 × 8000 that is equal 15928000

= 17901081
