Alright, let's work through 7801 times 5151 step by step
7801 × 5151 = 5151 × (7801)
+ 5151 × 1 which equals 5151
+ 5151 × 00 which equals 0
+ 5151 × 800 what gives us 4120800
+ 5151 × 7000 which equals 36057000

= 40182951
