Determining moler internal energy of helium

Question

Solve the following problem:

A thick-walled insulated metal chamber contains n_i, moles of helium at high pressure P_i. It is connected through a valve with a large, almost empty gasholder in which the pressure is maintained at a constant value P, very nearly atmospheric. The valve is opened slightly, and the helium flows slowly and adiabatically into the gasholder until the pressure on the two sides of the valve is equalized. Prove that

n_f/n_i = h’ - u_i/h’ - u_f ,

where

n_f = number of moles of helium left in the chamber

u_i = initial moler internal energy of helium in the chamber

u_f = final moler internal energy of helium in the chamber, and

h’ = u’ + P’v(where u’ = moler internal energy of helium in the  gasholder; v’ = moler volume of helium in the gasholder).