Solve the following 0-1 integer programming problem by implicit enumeration:
Maximize Sx1 + Sx2 + 8x3 + 2x4 + 4xs subject to -3x1 + 6x2 - x3 + 9x4 + 9xs ≤ 210, x1 + 2x2 + x3 + x4 - 3xs < 0, x1, x2, x3, x4, xs ∈ {0,1}
(Hint: Start with xs and then x3)