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;