Alright, let's work through 6641 times 3813 step by step
6641 × 3813 = 3813 × (6641)
+ 3813 × 1 which equals 3813
+ 3813 × 40 that is equal 152520
+ 3813 × 600 which equals 2287800
+ 3813 × 6000 what gives us 22878000

= 25322133
