At a game of billiards, A can give B 6 points in 50 and he can give C 13 in 65. In a game of 55, number of points B can give C is:

In a game of 50.
While A scores 50, B scores 50 - 6 = 44 and in a game of 65. While A scores 65, C scores 65 - 13 = 52.
∴ While A scores 50, C scores 52 / 65 × 50 = 40.
∴ While B scores 44, C's score = 40.
While B scores 55, C's score = 40 / 44 × 55 = 50.
∴ In a game of 55,
B can give C 55 - 50 = 5 points.