Answer:
9 or 3.8x10^-6
Step-by-step explanation:
By flipping a coin you'd look at how many times a head could appear (1/2) and multiply that by the 18 times.
Another explanation:
I'm not sure on this but would you raise 1/2 to the 18th power?
Divide everything by 8: 550/8=68.75, 250/8=31.25. The new dimensions are 68.75 inches by 31.25 inches :)
At around 20'000ft. and higher.