Task: Question Answering
Input (English): Problem: pipe a fills a tank of capacity 800 liters at the rate of 40 liters a minute. another pipe b fills the same tank at the rate of 30 liters a minute. a pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. if pipe a is kept open for a minute and then closed and pipe b is open for a minute and then closed and then pipe c is open for a minute and then closed and the cycle is repeated, when will the tank be full ?
Options: a. 48 minutes, b. 14 minutes, c. 39 minutes, d. 40 minutes 20 seconds, e. none of these
Output (English): a