PROC IML;
premix_p =   1.00;                     
total    = 500.00;                     
feed     = TOTAL - TOTAL*PREMIX_P/100; 
                                       
                   
A = { 1    1,                          
      0.44 0.08};                      
                                                                        
b={0,
   0};                                 
b[1,1]=1.00*feed;                      
b[2,1]=0.18*total;                     
z=inv(A)*b;                            
print A, b, x;
run;