6-71 A thin-walled double-pipe counter-flow heat exchanger is used to cool oil (cp=2.20kJ/kgC) from 150 to 40C at a rate of 2kg/s by water (cp=4.18kJ/kgC) that enters at 22C at a rate of 1.5kg/s. Determine the rate of heat transfer in the heat exchanger and the exit temperature of water. Consider the heat exchanger to be insulated externally