If the line spectrum of lithium has a red line at 670.8 nm. How much energy does a a photon with this wavelength have?

We already know the formula for finding the energy of a photon with this wavelength as:

E = ħc / λ

The information's that we already know are:

h = Plancks constant

= 6.626x10^-34 Js

c = light speed

= 2.999x10^8 m/s

λ = Wavelength of the light as given in the question

= 670.8x10^-9 m

E = amount of energy

Then

E = (6.626x10^-34) * (2.999x10^8) / (670.8x10^-9)

= 2.962x10^-19 J