Task: Question Answering
Input (English): Problem: p , q and r together earn rs . 1800 in 9 days . p and r can earn rs . 600 in 5 days . q and r in 7 days can earn rs . 910 . how much amount does r can earn per day ? 
Options: a ) s . 50 , b ) s . 70 , c ) s . 90 , d ) s . 100 , e ) s . 120
Output (English): a