Help i cant do this question a-level aqa a physics unit 5 old spec

I can try to help, no guarantees though, I'm rustier than a Soviet-era nail.

1600E6 Joules per second at about 25% efficiency equates to a total output (with regard to reactions) of 6.4E9 Joules per second.
Divide that by our value for the energy per fission event, we get the total number of fission events, let's just call that N.
Multiply that value by the mass of each U235 atom. I'm not a chemist, so for the mother of lord correct me if I'm wrong, but there is some formula with one mol of U235 being 235 grams, so, just do N divided by the Avogadro constant to find the number of mols, then multiply that by 0.235 for the total mass of the U235 that has been used.

That's the total mass of the U235 that has been used. Since the fuel consists 3% U235 and 97% U238, we have 3% of the mass. Divide our value by three, multiply by 100, and we have the total mass of the fuel.

Hope I helped... somewhaT?

Edit : Yikes that somewhaT typo xD