The average score of former 10 players is a, and the total score of former 10 players is 10a.

The average score of the top 8 masters is B, and the sum of the top 8 scores is 8b.

So the total score of the 9th, 10 is (10a-8b).

If the ninth player scores more C points than the10th player, let the10th player score X,

There is an equation X+X+c= 10a-8b.

Solution: X=( 10a-8b-c)/2.