Task: Question Answering
Input (English): Problem: working alone, a can complete a certain kind of job in 3 hours. a and d, working together at their respective rates, can complete one of these jobs in 2 hours. in how many hours can d, working alone, complete one of these jobs ?
Options: a. 2, b. 4, c. 6, d. 8, e. 10
Output (English): c