Pour out enough cider to make room in the glass jug for the concentrate and the sugar and the re-hydrated yeast (I would recommend using champagne yeast). Mix thoroughly and put an airlock on it. Come back about a week later, check the gravity and if it bottoms out, prime it with 1/5 of 3/4 cup of white sugar, then bottle it in two 2-liter plastic soda bottles, well-cleaned, of course. Let it condition for about a week and...enjoy!