[ Eq(1*k21*x1 + 1*k21*x2 + 1*k21*x3 + 1*k21*x4, k21*k22),
  Eq(1*k21*x5 + 1*k21*x6, k21*k23),
  Eq(1*k21*x5 + 1*k21*x9 + 1*k21*x10, k21*k24),
  Eq(1*k21*x7 + 1*k21*x8, k21*k25) ]