Alright, let's work through 3420 times 8678 step by step
3420 × 8678 = 8678 × (3420)
+ 8678 × 0 producing 0
+ 8678 × 20 that is equal 173560
+ 8678 × 400 what gives us 3471200
+ 8678 × 3000 what gives us 26034000

= 29678760
