The inelastic mean free path of electrons in a solid, , governs the surface sensitivity of techniques

The inelastic mean free path of electrons in a solid, λ, governs the surface sensitivity of techniques such as AES and XPS. The electrons generated below the surface must make their way to the surface without losing energy in order to give elemental and chemical shift information. An empirical expression for elements that give λ as a function of the kinetic energy of the electron generated in AES or XPS is λ = 538E⁻² + 0.41(lE)^0.5. The units of λ are mono-layers, E is the kinetic energy of the electron in eV, and l is the monolayer thickness in nano-meters. On the basis of this equation, what kinetic energy maximizes the surface sensitivity for a mono-layer thickness of 0.3 nm? An equation solver would be helpful in obtaining the answer.