Alright, let's work through 9940 times 8391 step by step
9940 × 8391 = 8391 × (9940)
+ 8391 × 0 producing 0
+ 8391 × 40 giving us 335640
+ 8391 × 900 producing 7551900
+ 8391 × 9000 that is equal 75519000

= 83406540
