Task: Question Answering
Input (English): Problem: on a trip , a cyclist averaged 9 miles per hour for the first 18 miles and 10 miles per hour for the remaining 12 miles . if the cyclist returned immediately via the same route and took a total of 7.2 hours for the round trip , what was the average speed ( in miles per hour ) for the return trip ? 
Options: a ) 6.9 , b ) 7.2 , c ) 7.5 , d ) 7.8 , e ) 8.1
Output (English): c