$${E_x - E_0 = hf = \frac{hc}{\lambda} \\ = \frac{(6,63 \times 10^{-34}\, \mathrm{J \cdot s})(3,00 \times 10^8\, \mathrm{m/s})}{(550 \times 10^{-9}\, \mathrm{m})(1,60 \times 10^{-19}\, \mathrm{J/eV})} \\ = 2,26\, \mathrm{eV}}$$