Alright, let's work through 3971 times 6491 step by step
3971 × 6491 = 6491 × (3971)
+ 6491 × 1 that results in 6491
+ 6491 × 70 giving us 454370
+ 6491 × 900 that equals 5841900
+ 6491 × 3000 resulting in 19473000

= 25775761
