The answer is B, 1,365.
The combination formula nCr=n!(n−r)!(r!)
n is the number of elements (total).
r is the number of elements picked from the set.
In this case, n = 15 and r = 4
15!(11!)(4!)
=1365
So, there are 1365 ways of listening to the CD's.
Hope I helped!
