Alright, let's work through 6639 times 5400 step by step
6639 × 5400 = 5400 × (6639)
+ 5400 × 9 which equals 48600
+ 5400 × 30 yielding 162000
+ 5400 × 600 yielding 3240000
+ 5400 × 6000 that results in 32400000

= 35850600
