Alright, let's work through 3899 times 6449 step by step
3899 × 6449 = 6449 × (3899)
+ 6449 × 9 that is equal 58041
+ 6449 × 90 producing 580410
+ 6449 × 800 producing 5159200
+ 6449 × 3000 which equals 19347000

= 25144651
