These three statements are all true: $9\times 9+7=88,98\times 9+6=888$ and $987\times 9+5=8888$. Carrying the same pattern one step further, what does $9876\times 9+4$ come to?

Each line has one more digit on the left and one more 8 in the answer: 88, then 888, then 8888, so the next answer has five 8s. Working it out confirms this: $9876\times 9=88884$ and 88884 + 4 = 88888. The traps: 8888 just repeats the previous line's answer, 88884 stops at the multiplication and forgets to add the 4, and 888888 jumps two steps by adding two more 8s instead of one.