If I've understood the rules correctly, France have to:

1. Win.

2. Score 4 tries for a bonus point

3. Beat Scotland by at least 21 points as Wales' current points difference (61) is 20 better than France's (41).

4. In the event of points and points difference being equal, then the number of tries scored comes into play. Wales have scored 20 to Frances 15.

If points, points difference and the number of tries are equal, then the championship is shared.