min: 3 x1 + 2 x2 + 5 x3 + 9 x4 + 4 x5;
 9 x1 + 3 x2 + 5 x3 + 2 x4 +   x5 = 14;
 2 x1 + 7 x2 + 3 x3 + 4 x4 + 3 x5 = 26;
 4 x1 + 2 x2 + 3 x3 + 6 x4 + 2 x5 = 13;