The LMTD for the heat exchanger is

Question

In a counter flow heat exchanger, hot fluid enters at 65⁰C and old fluid leaves at 30⁰C. mass flow rate of the hot fluid is 1 kg/s and that of cold fluid is 2 kg/s. specific heat of the hot fluid is 10 kJ/kgK and that of cold fluid is 5 kJ/kgK. The LMTD for the heat exchanger is             

      (a) 15                              (b) 30                           (c) 35                              (d) 45