The answer is approximately 11.18.
We can tell this is an isosceles triangle due to the sticks meaning the base angles are equal so the measurement of ACB would be the same as ABC so it would measure x
We need to count the number of games that score 15, 16, 17 and 18
Score 15 = 3 games
Score 16 = 2 games
Score 17 = 5 games
Score 18 = 3 games
Total = 13 games