Task: Question Answering
Input (English): Problem: john can complete a given task in 10 days. jane will take only 20 days to complete the same task. john and jane set out to complete the task by beginning to work together. however, jane was indisposed 4 days before the work got over. in how many days did the work get over from the time john and jane started to work on it together ?
Options: a. 8, b. 9, c. 8.5, d. 9.5, e. 10.5
Output (English): c