Counting & ProbabilityChallengeIdentities and Techniques, Proved ShareIdentities and Techniques, Proved · Challenge problemHow many 4-element subsets {a<b<c<d}\{a<b<c<d\}{a<b<c<d} of {1,2,…,15}\{1,2,\ldots,15\}{1,2,…,15} satisfy d−a≤8d-a\le 8d−a≤8?Check Show answer Walk through it step by step Practice more like this Review this concept