Alright, let's work through 1620 times 7631 step by step
1620 × 7631 = 7631 × (1620)
+ 7631 × 0 that results in 0
+ 7631 × 20 giving us 152620
+ 7631 × 600 giving us 4578600
+ 7631 × 1000 what gives us 7631000

= 12362220
