Total number of balls in the bag =6+9=15.
Number of white balls =6.
Number of black balls =9.
Four balls are drawn at random at a time.
The probability that first draw give four white balls
C415C46=911
The balls are not replaced.
Now, the probability that second draw give four black balls
C411C49=5521
The probability that the first draw give four white balls and second draw give four black balls
=911×5521=7153
Hence, the required probability is 7153.