Task: Question Answering
Input (English): Problem: working alone at their respective constant rates , a can complete a task in ‘ a ’ days and b in ‘ b ’ days . they take turns in doing the task with each working 2 days at a time . if a starts they finish the task in exactly 12 days . if b starts , they take half a day more . how long does it take to complete the task if they both work together ? 
Options: a ) 4 , b ) 4.5 , c ) 6 , d ) 8 , e ) 6.5
Output (English): c