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.
O]=4,227.58 kg; V[O2
Looks like it agrees completely with your calculations.
I can clarify any part of my method if someone wants.