Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: two pipes p and q can fill a cistern in 12 and 13 minutes respectively . both are opened together , but at the end of 3 minutes the first is turned off . how much longer will the cistern take to fill ?
3 / 4
1 minute and 39 seconds. (or 89/3 minutes if you prefer)