Alright, let's work through 8309 times 8391 step by step
8309 × 8391 = 8391 × (8309)
+ 8391 × 9 what gives us 75519
+ 8391 × 00 yielding 0
+ 8391 × 300 what gives us 2517300
+ 8391 × 8000 yielding 67128000

= 69720819
