Alright, let's work through 6638 times 6931 step by step
6638 × 6931 = 6931 × (6638)
+ 6931 × 8 that results in 55448
+ 6931 × 30 what gives us 207930
+ 6931 × 600 that is equal 4158600
+ 6931 × 6000 yielding 41586000

= 46007978
