Radiative transfer

[captain.joco]

1. The problem statement, all variables and given/known data
A galaxy consist of a uniform slab of stars mixed with dust. The slab has thickness L, and optical depth \tau for a ray passing perpendicularly through the slab. assume the emmisivity of the stars \epsilon and the density of dust is constand throught the slab. Further assume that no scattering occurs due to the dust.

Hence, calculate the surface brightness observed as function of inclination and show that it is independent of inclination if the ammount of dust becoms very large.

Can I get some help please in how to set the problem up?

Thanks