All daily challenges are solvable. They all come from a pool of Winning Deals and have game numbers associated with them. Some are easy, some are difficult so keep trying to solve it. If you are stuck, you can press the leaderboard option of the Daily prompt, then press the Show Me How To Win button, which will play the game for you.
The Daily Challenges are separate than your normal play, so you can do a Daily Challenge and after that is completed you go right back to your Standard game play.