An oil having a specific heat of 1880 J/kg · K enters a single-pass counter flow heat exchanger at a rate of 2 kg/s and a temperature of 400 K. It is to be cooled to 350 K. Water is available to cool the oil at a rate of 2 kg/s and a temperature of 280 K. Determine the surface area required if the overall heat transfer coefficient is 230 W/m² · K.