**Answer 1**

Using the equation E = hc/λ we can find out how much energy a single photon of wavelength 555nm has.

E = Planck Constant * Speed of Light/555nm = 3.579*10^-19 J

The number of photons will be total energy over the energy per photon

n = 4.85*10^-3/3.579*10^-19 = 1.355*10^16 photons

Source(s): http://www.wolframalpha.com/input/?i=Planck+Consta…

http://www.wolframalpha.com/input/?i=4.85mJ%2F%28P…

**Answer 2**

555 Nm