[20] Definitions for this question: - For a finite subset of the natural numbers SN,S is the sum of the elements of S. For example, {0,4,10}=14. If S=, then S=0. - Given a set AN and a number sN such that As, a set BA is a "just big enough subset of A to reach s " if both of the following properties are true: (i) Bs (ii) xB(B)x