Alright, let's work through 3903 times 6390 step by step
3903 × 6390 = 6390 × (3903)
+ 6390 × 3 yielding 19170
+ 6390 × 00 giving us 0
+ 6390 × 900 that equals 5751000
+ 6390 × 3000 yielding 19170000

= 24940170
