OK I got 27.3% for problem 2 #3 and 4(a) I got 3.47*10^7 m^3 for O2, and 4.26*10^7 kg not sure if correct.... anyone attempt these ones yet?

OK so I just saw that actually we are given the solar energy available so we can calculate it. I don't think it's that vague.

2.4.a. N[photons]=8.53881·10

^{33}; m[CH

_{2}O]=4.2574·10

^{7} kg; V[O

_{2}]=3.46704·10

^{7} m

^{3}.

2.4.b. N[photons]=8.47896·10

^{29}; m[CH

_{2}O]=4,227.58 kg; V[O

_{2}]=3,442.7 m

^{3}.

Looks like it agrees completely with your calculations.

I can clarify any part of my method if someone wants.