Alright, let's work through 80815103 times 99678134 step by step
80815103 × 99678134 = 99678134 × (80815103)
+ 99678134 × 3 producing 299034402
+ 99678134 × 00 resulting in 0
+ 99678134 × 100 yielding 9967813400
+ 99678134 × 5000 resulting in 498390670000
+ 99678134 × 10000 which equals 996781340000
+ 99678134 × 800000 yielding 79742507200000
+ 99678134 × 0000000 producing 0
+ 99678134 × 80000000 yielding 7974250720000000

= 8055498666057802
