Alright, let's work through 6720 times 615 step by step
6720 × 615 = 615 × (6720)
+ 615 × 0 giving us 0
+ 615 × 20 producing 12300
+ 615 × 700 yielding 430500
+ 615 × 6000 giving us 3690000

= 4132800
