Question

water is 88.8% by mass oxygen. How many grams of water would contain 2.25kg of oxygen?

Answer 1

0.888*?g H2O = 2250g
Solve for ?g

Answer 2

I need answer using conversion factors

Answer 3

The above is for 2250 g O atoms, not O2. Oxygen is 88.8% H2O by (16/18.015)*100 = 88.815%.
2250 g O x (1 mol H2O/1 mol O atoms) x (molar mass H2O/1 mol H2O) x (1 mol O atoms/atomic mass O) = ? g H2O for 2250 g O atoms. If you want 2250 g O2 you will need to correct for that.