# Energy needed to liberate electron from infinite potential well

I've been mulling over this for a while and getting nowhere.

Here is the question: an electron is bound in a square well of width $1.95\:\mathrm{nm}$ and depth $U = 6E_∞$. If the electron is initially in the ground level and absorbs a photon, what maximum wavelength can the photon have and still liberate the electron from the well?

In order to find the wavelength I need the energy difference between $U$ and $E_1$. The thing that confuses me the most is that according to the solutions, $E_1 = 0.625E_∞$. How do you find this?

Using the formula $E = n^2h^2/8mL^2$ I have $E_1 = 1.58 \times 10^{-20}\:\mathrm{J}$. What am I missing?

But the problem posed is very much a finite potential well of potential depth $U$. In this scenario, which means you need to find expressions for the wave function both inside and outside the square well (rather than just inside, for the infinite square well) and to have them connect smoothly (same value of the wave function at $x=\pm\frac{width}{2}$).