One kg of air under goes irreversible process between equilibrium state 1 and equilibrium state 2.

Question

One kg of air (R= 287 J/kg-K) under goes irreversible process between equilibrium state 1 (20⁰C, 0.9 m³) and equilibrium state 2 (20⁰C, 0.6 m³). The change in entropy s₂ – s₁ (in J/kg-K) is______