Alright, let's work through 15829381 times 42215121 step by step
15829381 × 42215121 = 42215121 × (15829381)
+ 42215121 × 1 producing 42215121
+ 42215121 × 80 resulting in 3377209680
+ 42215121 × 300 producing 12664536300
+ 42215121 × 9000 resulting in 379936089000
+ 42215121 × 20000 resulting in 844302420000
+ 42215121 × 800000 that is equal 33772096800000
+ 42215121 × 5000000 giving us 211075605000000
+ 42215121 × 10000000 producing 422151210000000

= 668239234270101
