<pre> Tableau #3 x y z s1 s2 r 1 0 1 1/5 2/5 0 13 0 1 0 -2/5 1/5 0 2 1 0 0 0 1 1 28 </pre> RREF has to get you to this. When you read the first two lines (the important ones since r=0), you know: x+z=13 y=2 <-- Isolated for you. but then you have the last row (r=1) which is the maximized result. So use z-13=x and y=2 in R=28. Get the z. Now get the x. You're done.