Alright, let's work through 3999 times 7720 step by step
3999 × 7720 = 7720 × (3999)
+ 7720 × 9 what gives us 69480
+ 7720 × 90 which equals 694800
+ 7720 × 900 what gives us 6948000
+ 7720 × 3000 resulting in 23160000

= 30872280
