In a counter-flow double-pipe exchanger oil is cooled from 85 °C to 57 °C by water entering at 25 °C. Oil 26 L/min, c = 1.95 kJ/kg·°C, specific gravity 0.85; water 15 L/min, c = 4.2 kJ/kg·°C; U = 300 W/m^{2}·°C. Find the heat-transfer area. (answer in m^{2})