Over time the cold water got warmer because it was room temperature.
Over time the warm water got colder because it reached room temperature.
The temperatures got closer together because they were both room temperature.
After 15 minutes the lines were touching and the temperatures were the same.
The room temp and the warm water surrounding it made it hotter.
The opposite, the room temp and the cold water surrounding it.
The temp would be about 55 degrees.
Yes, because it proved the water didn't mix, just heat was flowing.