Alright, let's work through 5128 times 7857 step by step
5128 × 7857 = 7857 × (5128)
+ 7857 × 8 what gives us 62856
+ 7857 × 20 which equals 157140
+ 7857 × 100 that results in 785700
+ 7857 × 5000 which equals 39285000

= 40290696
