Task: Question Answering
Input (English): Problem: a can complete a project in 20 days and b can complete the same project in 40 days. if a and b start working on the project together and a quits 10 days before the project is completed, in how many days will the project be completed ?
Options: a. 18 days, b. 20 days, c. 26.67 days, d. 16 days, e. 12 days
Output (English): b