Alright, let's work through 3870 times 7870 step by step
3870 × 7870 = 7870 × (3870)
+ 7870 × 0 what gives us 0
+ 7870 × 70 that is equal 550900
+ 7870 × 800 what gives us 6296000
+ 7870 × 3000 giving us 23610000

= 30456900
