A double pipe heat exchanger is to be designed to heat 1 kg/s of a cold fluid from 30°C to 60°C using 2 kg/s of a hot fluid at 100°C. The two streams have equal specific heat capacities and overall heat transfer coefficient. Calculate the ratio of heat transfer areas of counter current to co-current. a) 1.142 b) 0.875 c) 0.927 d) 1.077