Hot oil is to be cooled in a double-tube counter flow heat exchanger. The copper inner tubes have a diameter of 2 cm and negligible thickness. The inner diameter of the outer tube (the shell) is 3 cm. Water flows through the tube at a rate of 0.5 kg/s, and the oil through the shell at a rate of 0.8 kg/s. Taking the average temperatures of the water and oil to be 45 degrees Celsius and 80 degrees Celsius, respectively, determine the overall heat transfer coefficient of this heat exchanger. Include diagram.