Water (\(C_{\text{p}} = 4.18\text{ kJ/kg}\cdot\text{K}\)) at \(80^\circ\text{C}\) enters a counter-flow heat exchanger with a mass flow rate of \(0.5\text{ kg/s}\). Air (\(C_{\text{p}} = 1\text{ kJ/kg}\cdot\text{K}\)) enters at \(30^\circ\text{C}\) with a mass flow rate of \(2.09\text{ kg/s}\). If the effectiveness of the heat exchanger is 0.8, the LMTD (\(^\circ\text{C}\)) is