Powering LED Strips greater than 5 Meters long?
Without having extremely detailed specifications of the LED strip and what you consider to be acceptable the answer cannot be determined.

Connect it to the end and see if it gives acceptable performance, I would expect that it will. if it does not (light too dim at the far end) you can then add a cable from the junction, (or move the power suppply to the junction) etc.. use a 12V power supply capable of 7.5A pr more,  there's no simple way to use 24V with that setup.

ideally you should connect power to the strip at several points.

eg: by running a cable parallel with the strip

You may find that it's possible to drill a series of holes in the ceiling and fish the supply cable through them, and then fix the led strip such that it conceals the holes