Two buses leave a station at the same time and travel in opposite directions. One bus travels 10 mih faster than the other. If the two buses are 504 miles apart after 4 hours, what is the rate of each"

a) 120 mph and 110 mph
b) 130 mph and 120 mph
c) 140 mph and 130 mph
d) 150 mph and 140 mph