Double pipe heat exchanger

Question

In a double pipe heat exchanger, M_h C_h = 0.5 M_cC_c, ‘M’ denotes mass flow rate (kg/s), ‘C’ denotes specific heat (J/kg K), and suffix ‘h’ and suffix ‘c’ denote hot and cold fluid, respectively. The hot and cold fluids enter the heat exchanger at temperatures T_h1 and T_c1, respectively.  Deduce an expression, in terms of T_h1 ,  T_c1 and T_h2 , for the ratio of the area of a counter-flow exchanger to that of a parallel flow exchanger which will give the same hot fluid outlet temperature T_h2. What is this ratio if T_h1 = 150°C,
T_c1 = 30°C and T_h2 = 90°C?