A shell-and-tube heat exchanger is to be designed to cool down the petroleum-based organic vapor available at a flow rate of 5 kg/s and at a saturation temperature of 75°C. The cold water (c_p = 4187 J/kg · K) used for its condensation is supplied at a rate of 25 kg/s and a temperature of 15°C. The cold water flows through copper tubes with an outside diameter of 20 mm, a thickness of 2 mm, and a length of 5 m. The overall heat transfer coefficient is assumed to be 550 W/m² · K and the latent heat of vaporization of the organic vapor may be taken to be 580 kJ/kg. Assuming negligible thermal resistance due to pipe wall thickness, determine the number of tubes required.