Gemini 2.5 Pro nails it, as far as I'm concerned:

This sounds like a bit of a riddle! Here's how to think about it:

If you can dry all the towels at the same time: For example, if you have a large enough dryer or enough space on a clothesline, adding more towels doesn't necessarily increase the drying time.

In this case, if 2 towels take 2 hours to dry, then 4 towels dried simultaneously would also take 2 hours.

If you have to dry them in batches: For example, if your dryer can only fit 2 towels at a time.

You would dry the first 2 towels (2 hours). Then you would dry the second 2 towels (another 2 hours). In this scenario, it would take 4 hours in total.

Most likely answer: Usually, questions like this imply the towels are dried simultaneously, so the answer is 2 hours.