A thin-walled double-pipe, counter-flow heat exchanger is to be used to cool oil (cp = 2.2 kJ/kgdegC) from 150oC to 40oC at a rate of 2.3 kg/s by water (cp = 4.18 kJ/kgoC) that enters at 20degC at a rate of 1.4 kg/s. The diameter of the tube is 13 cm and its length is 60 m. Determine the overall heat transfer coefficient of this heat exchanger using (a) LMTD and (b) -NTU method.