Alright, let's work through 7890 times 9966 step by step
7890 × 9966 = 9966 × (7890)
+ 9966 × 0 producing 0
+ 9966 × 90 resulting in 896940
+ 9966 × 800 that equals 7972800
+ 9966 × 7000 giving us 69762000

= 78631740
