Using the solver and putting the condition on all Decision Variable must be integer:
18 20 0 Objective 94
x1 x2 x3
3 2 0
8 16 4 464 <= 490
20 12 0 600 <= 600
Solution x1= 18
x2= 20
x3 = 0
while with no integer constraint:
16.60714 22.32143 0 Objective 94.46429
x1 x2 x3
3 2 0
8 16 4 490 <= 490
20 12 0 600 <= 600
Objective Cell (Max)
Cell Name Original Value Final Value
$F$2 Objective 94 94.46428571
Variable Cells
Cell Name Original Value Final Value Integer
$B$2 18 16.60714286 Integer
$C$2 20 22.32142857 Integer
$D$2 0 0 Integer
Constraints
Cell Name Cell Value Formula Status Slack
$E$5 Objective 490 $E$5<=$G$5 Binding 0
$E$6 Objective 600 $E$6<=$G$6 Binding 0
$B$2:$D$2=Integer