steam power plant cycle design, Mollier Diagram help

Blaine

Hello All,
I am currently trying to optimize a steam power plant cycle and I am stuck... What I am unable to figure out is how to use a Mollier chart/diagram in order to determine the amount of steam I must tap off from my turbine to my feed water heater. I know my feed water heaters inlet and outlet temperatures, mass flow rate, TTD and DCA. I have drawn en expansion line in my Mollier chart, taking into consideration my isentropic efficiency. I have been told that from that line I should be able to make an energy balance and directly read off the both the bleed temperature and pressure and enthalpy of my steam to my feed water heater. Could someone please shed some light on the matter?? Regards Blaine