Alright, let's work through 6431 times 8040 step by step
6431 × 8040 = 8040 × (6431)
+ 8040 × 1 which equals 8040
+ 8040 × 30 resulting in 241200
+ 8040 × 400 which equals 3216000
+ 8040 × 6000 resulting in 48240000

= 51705240
