3. A U-tube multi-tubular heat exchanger as shown in the figure below is used to cool 5.5 kg/s of oil flow from 380 K to 320 K. Oil flows through the shell outside the tube, and 280 K of cooling water flows through 16 tube bundles with an inner diameter of 15 mm. Calculate the temperature of the coolant, assuming that the average specific heat of oil and water is 2.122 and 4.180 kJ/kgK, respectively