Ok so basically you need to put numbers in front of each chemical compound/element to make sure there is the same number of each element/compound before and after the reaction.
For example:
#4: _Ag2O -> _Ag + _O
As you can see in the pre-reaction compound, there are 2 Ag and 1 O. The compound undergoes decomposition to become Ag+ O. HOWEVER, the law of conservation of mass states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system's mass cannot change, so quantity cannot be added nor removed.
Basically there must be equal amounts of everything on both sides of the equation.
So, knowing that, since there are 2 She's and 1 O on the pre-reaction side there must be 2 Ag's and 1 O on the post-reaction side.
So the answer would be
Ag2O -> 2Ag + 1O