Determine the energy and number of configurations

[rmjmu507]

Homework Statement

N surfactant molecules occupy an interface with A binding sites. The molecule has energy= -ε when perpendicular to the interface, and -δ when parallel to the interface (ε>δ>0). M is the number of surfactants perpendicular to the interface.

For a given value of M, determine the energy E(M) and the number of configurations $\Gamma$(M)

Homework Equations

None that I know of...

The Attempt at a Solution

I don't even know where to begin. Any advice or direction much appreciated.

 

[mfb]

If M molecules are perpendicular to the interface and have an energy -ε each, how many of the N molecules are parallel and have an energy -δ each? What is the total energy of all molecules together?
In how many ways can you choose M particles out of N?