Alright, let's work through 1591 times 3990 step by step
1591 × 3990 = 3990 × (1591)
+ 3990 × 1 producing 3990
+ 3990 × 90 resulting in 359100
+ 3990 × 500 that results in 1995000
+ 3990 × 1000 what gives us 3990000

= 6348090
