Solve each of the following discrete optimization models by total enumeration.

(a) min 2x1 + x2 + 4x3 + 10x4 s.t. x1 + x2 + x3 … 2 3x1 + 7x2 + 19x3 + x4 Ú 20 x1, x2, x3 = 0 or 1 x4 Ú 0

(b) max 30x1 + 12x2 + 24x3 + 55x4 s.t. 30x1 + 20x2 + 40x3 + 35x4 … 60 x2 + 2x3 + x4 Ú 2 x1 Ú 0 x2, x3, x4 = 0 or 1