If the initial beam has 1x1018 photons ( Io= 1 x 1018) and the absorbance is 0.680, then

A = log (Io/I)

antilog 0.680 = 1 x 1018 photons / I

I = 2.09 x 1017 photons

Therefore the number of photons transmitted is 2.09 x 1017.

What is the wavelength of the transmitted photons?

1)  longer than the initial beam.
2)  the same as the initial beam.
3)  shorter than the initial beam.