A strings of length $8$ using the letters x and y only
1) How many of these strings have exactly $3$ x's? So it's $\binom{8}{3} = 56$
2) How many of these strings have 3 x's in a row?
I don't know how to handle that case, so for that one the order matters. So in my opinion it should contain $P(8,3) = 8 \times 7 \times 6 = 336$. But I should have something to deduct from that, I am confused.
Thank you!