Energy of the dust

Classical Mechanics Level 3

One thousand dust particles are trapped on a surface. The two states that a particle can occupy are

absorbed on the surface in a zero energy state.
excited with energy $E_1$ .

Suppose the particles are in thermal equilibrium at temperature $T$ , and 20 % of the particles are in the excited state. Find the value of $\frac{1}{k_BT}\sum_i E_i$

Details and Assumptions

The particles are identical.
$k_B$ is the Boltzmann constant.