Alright, let's work through 5142 times 3909 step by step
5142 × 3909 = 3909 × (5142)
+ 3909 × 2 what gives us 7818
+ 3909 × 40 which equals 156360
+ 3909 × 100 what gives us 390900
+ 3909 × 5000 giving us 19545000

= 20100078
