When 29.8 mole of aluminum reacts with excess oxygen according to the following reaction, how many moles of aluminum oxide can be produced?
4 al + 3 o2 → 2 al2o3

Use dimensional analysis.
first, you put 29.8 mole of Al at the top.
And, in the next column you put 2 mole of Al2O3 at the top and 4 mole of Al at the bottom.
Then, you multiply 29.8 and 2 and then divide by 4. that will give you the answer 14.9 mole of Al2O3.

It is called a neutralization reaction