The floor space in a certain market is

The floor space in a certain market is rented for $15 per 30 square feet for one day. In the market, Alice rented a rectangular floor space that measured 8 feet by 15 feet, and Betty rented a rectangular floor space that measured 15 feet by 20 feet. If each woman rented her floor space for one day, how much more did Betty pay than Alice? $27, $36, $54, $90, $180