Alright, let's work through 1251 times 5397 step by step
1251 × 5397 = 5397 × (1251)
+ 5397 × 1 that is equal 5397
+ 5397 × 50 yielding 269850
+ 5397 × 200 which equals 1079400
+ 5397 × 1000 which equals 5397000

= 6751647
