Answer
$flux = 5.89\times 10^{18}~photons/m^2~s$
Work Step by Step
In part (a), we found that photons are emitted at a rate of $~~2.96\times 10^{20}~photons/s$
We can find the surface area of a sphere of radius $r = 2.00~m$:
$A = 4\pi~r^2 = (4\pi)(2.00~m)^2 = (16.0~pi)~m^2$
We can find the photon flux:
$flux = \frac{2.96\times 10^{20}~photons/s}{(16.0~pi)~m^2} = 5.89\times 10^{18}~photons/m^2~s$
