Alright, let's work through 3989 times 5136 step by step
3989 × 5136 = 5136 × (3989)
+ 5136 × 9 that is equal 46224
+ 5136 × 80 producing 410880
+ 5136 × 900 that results in 4622400
+ 5136 × 3000 what gives us 15408000

= 20487504
