In order to determine the probability fr each case, it is necessary to calculate the quotient between the number of desired cases and the total number of options.
a) a white counter or a green counter
Consider that there are 9 white counters and 6 green counters, that is, there are 9 + 6 = 15 counters with some characteristic you want.
The total number of counters are 9 + 8 + 6 = 23 counters. Then, the probability is:
P = 15/23 it is not possible to simplify the fractions
b) a black counter or a green counter
There are 8 black counters and 6 green counters, that is, 8 + 6 = 14 counters.
The probability is:
P = 14/23 it is not possible to simplify the fraction
c) not a green counter
It means only white and black counter. Then, there are 9 + 8 = 17 counters with a desired characteristic. The probability is:
P = 17/23