$${\Phi = hf_0 = (6,63 \times 10^{–34}\, \mathrm{J \cdot s})(5,5 \times 10^{14}\, \mathrm{Hz}) \\ = 3,6 \times 10^{–19}\, \mathrm{J} = \underline{\underline{2,3\, \mathrm{eV}}}}$$