A control system is represented by below equations

y₂ = a₁₂ y₁ + a₃₂ y₃

y₃ = a₂₃ y₂ + a₄₃ y₄

y₄ = a₂₄ y₂ + a₃₄ y₃ + a₄₄ y₄

y₅ = a₂₅ y₂ + a₄₅ y₄

Then the Δ (in mason’s gain formula) for transfer function \(\frac{{{y_5}}}{{{y_1}}}\) is