Alright, let's work through 8939 times 8928 step by step
8939 × 8928 = 8928 × (8939)
+ 8928 × 9 giving us 80352
+ 8928 × 30 what gives us 267840
+ 8928 × 900 giving us 8035200
+ 8928 × 8000 that is equal 71424000

= 79807392
