Alright, let's work through 80345300 times 63900401 step by step
80345300 × 63900401 = 63900401 × (80345300)
+ 63900401 × 0 that results in 0
+ 63900401 × 00 yielding 0
+ 63900401 × 300 that results in 19170120300
+ 63900401 × 5000 that equals 319502005000
+ 63900401 × 40000 that results in 2556016040000
+ 63900401 × 300000 what gives us 19170120300000
+ 63900401 × 0000000 producing 0
+ 63900401 × 80000000 giving us 5112032080000000

= 5134096888465300
