Methane combusts with air in a furnace according to the reaction \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \). The heat of reaction \( \Delta H_{\text{rxn}} \) is -880 kJ per mol of CH4 and is assumed constant. The furnace is well-insulated, and no side reactions occur. All components behave as ideal gases with a constant molar heat capacity of 44 J mol\(^{-1}\) °C\(^{-1}\). Air is composed of 20 mol% O2 and 80 mol% N2. The air-fuel mixture enters the furnace at 50°C. The methane conversion \( X \) varies with the air-to-methane mole ratio \( r \) as \( X = 1 - 0.1 e^{-2(r-r_s)} \) with \( 0.9 r_s \leq r \leq 1.1 r_s \), where \( r_s \) is the stoichiometric air-to-methane mole ratio. For \( r = 1.05 r_s \), the exit flue gas temperature in °C, rounded off to 1 decimal place, is _____.