<s>[INST] # Problem
The binomial theorem states that for any positive integer n , ( x + y ) n = ∑ k = 0 n ( n k ) x n − k y k , where ( n k ) = n ! k ! ( n − k ) ! . If ( x + y ) 15 = ∑ k = 0 15 ( 15 k ) x 15 − k y k , what is ( 15 8 )?[/INST]