Task: Question Answering
Input (English): Problem: two pipes can fill a tank in 18 minutes and 6 minutes. an outlet pipe can empty the tank in 45 minutes. if all the pipes are opened when the tank is empty, then how many minutes will it take to fill the tank ?
Options: a. 1 / 15, b. 1 / 6, c. 1 / 11, d. 1 / 10, e. 1 / 12
Output (English): b