Energy of photon is given by formula
[tex]E = h\nu[/tex]
here
h = Planck's constant
[tex]h = 6.6* 10^{-34}[/tex]
[tex]\nu = frequency = 6 * 10^{20}Hz[/tex]
now the energy is given by
[tex]E = 6.6*10^{-34} * 6 * 10^{20}[/tex]
[tex]E = 3.96 * 10^{-13} J[/tex]
