Alright, let's work through 3137 times 3991 step by step
3137 × 3991 = 3991 × (3137)
+ 3991 × 7 that is equal 27937
+ 3991 × 30 what gives us 119730
+ 3991 × 100 resulting in 399100
+ 3991 × 3000 that results in 11973000

= 12519767
