Answer: 22,084,920 different clubs
Step-by-step explanation:
The club must have 6 juniors and 8 seniors
We have a total of 13 juniors and 16 seniors.
Now, we know that the possible combinations of N objects into a group of K is equal to:

For the juniors we have N = 13 and K = 6

For the seniors we have N = 16 and K = 8

Now, as the group consist on both combinations togheter, the number of different clubs that can be formed are:
C = Cj*Cs = 1,716*12,870 = 22,084,920