Thermodynamics: Brayton Refrigeration Cycle with Regenerator

[Robin Ghoul]

I have a brayton refrigeration cycle with a regeneator same as the picture below only with irreversible regenrator, compressor and turbine (And different values).

The given in my problem are:
Ti=0 C, T3= 35 C, T5= -80 C, mass flow rate m= 0.4 kg/s
Turbine efficiency Et=0.85, Compressor efficiency =0.8 and pressure ratio =5
I found h1=273.3 KJ/Kg, h2=552.27 KJ/Kg, h3= 308.5 KJ/Kg, h5=193 KJ/kg
I need to find the regenerator effectiveness
My question are:
1-How to find h4 and h6
2-What is the regenrator efficiency in this case I know if the regenerator was ideal the h4=h1, but I am unable to find the real h4, maybe it has to do with the turbine efficiency but I only have the real h5 I need h5s to find h4...
As fir the regenerator effectiveness I thought it would be Et=(h1-h3)/(h4-h3).. as h4 approaches h1, the effectiveness approaches 1

 

[Robin Ghoul]

Also, specific heats are at room temperature