Alright, let's work through 28780615 times 90103997 step by step
28780615 × 90103997 = 90103997 × (28780615)
+ 90103997 × 5 that results in 450519985
+ 90103997 × 10 that is equal 901039970
+ 90103997 × 600 resulting in 54062398200
+ 90103997 × 0000 giving us 0
+ 90103997 × 80000 which equals 7208319760000
+ 90103997 × 700000 yielding 63072797900000
+ 90103997 × 8000000 that is equal 720831976000000
+ 90103997 × 20000000 giving us 1802079940000000

= 2593248447618155
