/* Objective function */
min: 21 x1 + 20 x2 + 15 x3;

/* Variable bounds */
  5 x1 +  6 x2 +  3 x3 >= 120;
  5 x1 +  4 x2 +  5 x3 >= 100;
    x1                 <=  12;
            x2         <=  12;
                    x3 <=  12;
    x1 -    x2 -    x3 <=   0;

integer x1, x2, x3;