Water is boiled at 150°C in a boiler by hot exhaust gases (c_p = 1.05 kJ/kg · °C) that enter the boiler at 400°C at a rate of 0.4 kg/s and leaves at 200°C. The surface area of the heat exchanger is 0.64 m². The overall heat transfer coefficient of this heat exchanger is
(a) 940 W/m² · K

(b) 1056 W/m² · K

(c) 1145 W/m² · K

(d) 1230 W/m² · K

(e) 1393 W/m² · K