The Question is The rates of on-time flights for commercial jets are continuously tracked by the U.S. Department of Transportation. Recently, Southwest Air had the best reate with 80 % of its flights arriving on time. A test is conducted by randomly selecting 17 Southwest flights and observing whether they arrive on time.

(a) Find the probability that exactly 9 flights arrive late.

I came down to it being (17/!17!(17−9)!) *(2^9) *(8)^17−9

But it's getting marked wrong. The steps and answer would be greatly appreciated.