Task: Question Answering
Input (English): Problem: p and q can complete a work in 15 days and 10 days respectively . they started the work together and then q left after 2 days . p alone completed the remaining work . the work was finished in - - - days . 
Options: a ) 12 , b ) 16 , c ) 20 , d ) 24 , e ) 28
Output (English): a