Cold water (c_p = 4180 J/kg·K) leading to a shower enters a thin-walled double-pipe counter-flow heat exchanger at 15°C at a rate of 1.25 kg/s and is heated to 45°C by hot water (c_p = 4190 J/kg·K) that enters at 100°C at a rate of 3 kg/s. If the overall heat transfer coefficient is 880 W/m²·K, determine the rate of heat transfer and the heat transfer surface area of the heat exchanger.