Alright, let's work through 8458 times 991 step by step
8458 × 991 = 991 × (8458)
+ 991 × 8 yielding 7928
+ 991 × 50 yielding 49550
+ 991 × 400 giving us 396400
+ 991 × 8000 yielding 7928000

= 8381878
