> with(linalg);
> S := solve({x+20*y = 1000, 0.5e-1*x+2.1*y = 85});
                     {y = 31.81818182, x = 363.6363636}
> 20*32;
                                     640
> 1000-640;
                                     360
> 0.5e-1*360+2.1*32;
                                    85.20
>