Alright, let's work through 3993 times 4209 step by step
3993 × 4209 = 4209 × (3993)
+ 4209 × 3 what gives us 12627
+ 4209 × 90 resulting in 378810
+ 4209 × 900 that results in 3788100
+ 4209 × 3000 that results in 12627000

= 16806537
