Alright, let's work through 8609 times 999 step by step
8609 × 999 = 999 × (8609)
+ 999 × 9 that equals 8991
+ 999 × 00 that equals 0
+ 999 × 600 that equals 599400
+ 999 × 8000 giving us 7992000

= 8600391
