[Einstein Uae]

Dont forget the Ef is the fermi energy search for its equation in your textbook you will find and equation that have the effective mass in it.

Ec is the energy of the bottom of this band try to find it .

There is also another formula for the effective density of states at the bottom of the conduction band Nc find its equation and then find the value of h then substitute the value of h into fermi energy's equation and you get Ef .

Please if you have the question in english post it as fast as you can .