Can someone PLEASE help me with this problem, I’ve tried it multiple times and keep getting it wrong :(

Answer:
Explanation:
Okay.
From convervation of mass in chemical processes, all the reactants combined have the same mass as all the products.
m react = m prod
m Hg + m O 2 = m HgO + m O 2
114.0g+12.8g=123.1g+ m O 2
Solving for mO2 = 3.70 g
This is what I know.
I do hope I helped you! :)