Alright, let's work through 1991 times 9987 step by step
1991 × 9987 = 9987 × (1991)
+ 9987 × 1 giving us 9987
+ 9987 × 90 what gives us 898830
+ 9987 × 900 resulting in 8988300
+ 9987 × 1000 that results in 9987000

= 19884117
