How many grams of magnesium oxide can be produced when 97.2 g mg react with 88.5 g o2?

First we establish the chemical reaction equation. 
2Mg + O2 = 2MgO. 
Then we need to know which of the reactant is limiting. We do that by multiplying the number of moles of reactant to the stoichiomeric coefficient. For Magnesium: 97.2 g
For O2: 88.5g*
Since O2 has the smaller moles, this is the Limiting reactant. Then we solve basing on the number of O2 used. 

88.5g