I think one of the methods in solving this is taking 5280 x 36 = 19080 and then dividing that number by 60 because of 60 min in an hour. You then get 3,168 and divide that by 60 again but this time the 60 represents sec. In which case finally you get 52.8 feet per sec, and in 15 sec that would be 792 feet. Don't quote me but I believe if this isn't correct it's at least on the right track.
