Alright, let's work through 3390 times 6390 step by step
3390 × 6390 = 6390 × (3390)
+ 6390 × 0 that results in 0
+ 6390 × 90 yielding 575100
+ 6390 × 300 that is equal 1917000
+ 6390 × 3000 producing 19170000

= 21662100
