This is probably one of those dumb things where someone does it mathmatically and then erad posts "LOL NO EACH BUS SEAT HAS 4 LEGS AND THERE ARE 30 BUS SEATS LOLOLOLLOLOLOLLOL".
Anyway, without any of the retarded withholding-information crap, it should be:
7 * 2 + 7^3 * 4 + 7^4 * 4
...or 10990.