Identify the correct expression for the ratio of mass flow rates of two fluids A and B flowing through the heat exchanger of a binary vapor power cycle. Use the energy balance equation on the heat exchanger. Fluid A is the working fluid of the topping cycle and fluid B is the working fluid of the bottoming cycle. h1 and h2 are the enthalpies of fluid A at the inlet and the exit of the heat exchanger, respectively. h3 and h4 are the enthalpies of fluid B at the inlet and the exit of the heat exchanger, respectively.