Alright, let's work through 3811 times 5243 step by step
3811 × 5243 = 5243 × (3811)
+ 5243 × 1 that equals 5243
+ 5243 × 10 what gives us 52430
+ 5243 × 800 resulting in 4194400
+ 5243 × 3000 what gives us 15729000

= 19981073
