param N := 3;

var x{1..N};

minimize f:
-1*x[1]*x[2]*x[3];

subject to cons1:
x[1]+2*x[2]+2*x[3] >= 0;

subject to cons2:
72 - x[1] - 2*x[2] - 2*x[3] >= 0;

subject to cons3:
0 <= x[1] <= 20;

subject to cons4:
0 <= x[2] <= 11;

subject to cons5:
0 <= x[3] <= 42;

data;
var x:=
1	10
2	10
3	10;
solve;

display x;