@Carl Love yes,  it is,  sample is as given below, here is first data

with Optimization :

LPSolve(Z, {95x11 + 151x21 + 163x31 + 181x41 + 98x51 + 235x61 + 225x71 + 155x81 + 193x91 + 252xa1 + 264xb1 + 254xc1 + S11=95.00,87x11 + 52x21 + 56x31 + 75x41 + 68x51 + 95x61 + 90x71 + 84x81 + 101x91 + 108xa1 + 152xb1 + 123xc1 + S21=87.00,-16Z + 16x11 + 20x21 + 28x31 + 29x41 + 25x51 + 59x61 + 34x71 + 33x81 + 35x91 + 54xa1 + 56xb1 + 42xc1 + S31=0,-150Z + 150x11 + 132x21 + 162x31 + 169x41 + 162x51 + 259x61 + 236x71 + 208x81 + 247x91 + 271xa1 + 309xb1 + 285xc1 + S41=0} assume=nonnegative)