Alright, let's work through 1686 times 6738 step by step
1686 × 6738 = 6738 × (1686)
+ 6738 × 6 that results in 40428
+ 6738 × 80 yielding 539040
+ 6738 × 600 that results in 4042800
+ 6738 × 1000 what gives us 6738000

= 11360268
