82.5 g of silver oxide decomposed.
You're dealing with the decomposition reaction of silver oxide,
The balanced chemical equation for this reaction looks like this
You know that you have a
In order to determine how many moles of oxygen gas the reaction produced, use the ideal gas law equation
Notice that I converted the pressure from mmHg to atm.
If this many moles of oxygen were produced, then the number of moles of silver oxide that underwent decomposition was
To determine the mass in grams of silver oxide that contains this many moles, use the compound's molar mass