Alright, let's work through 3891 times 9478 step by step
3891 × 9478 = 9478 × (3891)
+ 9478 × 1 that is equal 9478
+ 9478 × 90 that is equal 853020
+ 9478 × 800 resulting in 7582400
+ 9478 × 3000 giving us 28434000

= 36878898
