Hot water is flowing at an average velocity of 1.5 m/s through a cast iron pipe (k 5 52 W/m·K) whose inner and outer diameters are 3 cm and 3.5 cm, respectively. The pipe passes through a 15-m-long section of a basement whose temperature is 15°C. If the temperature of the water drops from 70°C to 67°C as it passes through the basement and the heat transfer coefficient on the inner surface of the pipe is 400 W/m²·K, determine the combined convection and radiation heat transfer coefficient at the outer surface of the pipe.