Energy Collected in one pixel on a CCD.

There are two telescopes observing at night. The first telescope is 0.3m and has a focal ratio of f/8. The second telescope has a focal ratio of f/4 and is 30m in diameter. They each have an identical CCD camera whose pixels are 25 microns on a side. How much energy will be accumulated in a single pixel in a 100s exposure?

Note: Object being observed has an apparent brightness of 1.0*10^-7 W m^-2 and has an angular diameter of 15 arcsecsonds.

I have determined that the focal ratios of telescope 1= 2.4m and telescope 2 = 120m, and the the energy incident on one pixel:
=(1.0*10^-7)(2.5*10^-5)^2(100s)= 6.25*10^-10.

I have not taken into account the other variables above and I am not sure how to continue on from this point. Any help on this problem would be much appreciated.

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