The answer is "18480 feet".
Sound travels at 6160 feet in = 5.5 seconds
Then sound travels 1 feet in = 5.5/6160 = 0.00089285714 seconds
Now we have to find that how far does it travel in 16.5 seconds,
= 16.5 seconds / 0.00089285714 seconds = 18480.0000591 feet
= 18480 feet
