How much energy (in kj) do 3.0 moles of photons, all with a wavelength of 670 nm, contain? ?

Photon energy is the energy carried by a single photon with a certain wavelength and frequency. These terms are related by an equation. 
E = hv
where h is the Planck's constant (6.626 x 10-34 J s), v is the frequency which is related to the wavelength by:

λv = c where λ is the wavelength and c is the speed of light (3.00 x 108 m/s)

Therefore, the energy equation 
E = hc / λ
E = 6.626 x 10^-34 J s (3.00x10^8 m/s) / 670 x10^-9 m
E = 2.966865672x10^-19 J per photon

Total energy = 2.966865672x10^-19 J / photon ( 3.0 mol) ( 6.022x10^23 photon / 1 mol ) = 535993.95 J