Aluminum and oxygen gas react to produce aluminum oxide
Aluminium oxide is Al2O3, so there are 3 oxygen atoms for every 2 aluminium atoms. Divide 75 by the relative atomic mass of oxygen (15.9994). That is proportional to the number of oxygen atoms. Then divide by 3 and multiply by 2. This gives a number proportional to the number of aluminium atoms. Then multiply this by the relative atomic mass of aluminium (26.981529) to give the mass of aluminium required in grams.
