Alright, let's work through 3991 times 7629 step by step
3991 × 7629 = 7629 × (3991)
+ 7629 × 1 which equals 7629
+ 7629 × 90 what gives us 686610
+ 7629 × 900 that equals 6866100
+ 7629 × 3000 that results in 22887000

= 30447339
