Greetings!
To find this you could simply find the percentage of successful throws, to do this you simply divide the actual amount by the possible amount then multiply by 100.
9 ÷ 10 -= 0.9 x 100 = 90, so 90% of throws were successful.
10 ÷ 12 = 0.8333 x 100 = 83.33, so 83.33% of throws were successful.
This means that Keith had a higher percentage of successful throws so Keith is better at making throws.
Hope this helps!