[ 1*x[1] + 1*x[2] + 1*x[3] + 1*x[6] + 1*x[7] + 1*x[8] + 1*x[9] + 1*x[10] + 1*x[11] = k[18],
  1*x[4] + 1*x[6] + 1*x[7] = k[19],
  1*x[5] + 1*x[8] + 1*x[9] + 1*x[10] + 1*x[11] = k[20] ]