! Resnick, p 279, fertilizer blending
      max 20 x1 + 30 x2
 SUBJECT TO
     N)    .1 x1 + .075 x2 <= 1500
     P)   .08 x1 + .10  x2 <= 1200
     K)   .05 x1 + .15  x2 <= 1500
 END