Task: Question Answering
Input (English): Problem: pipe a fills a tank in 12 minutes. pipe b can fill the same tank 3 times as fast as pipe a. if both the pipes are kept open when the tank is empty, how many minutes will it take to fill the tank ?
Options: a. 4 mins, b. 6 mins, c. 5 mins, d. 3 mins, e. 7 mins
Output (English): d