Pt - platnium can conduct electricity and is inert and will not participate in any reaction
If you have an inert electrode, its the same as normal ones
Search for the half equation for Ag and Br
Ag+ + electrion --> Ag (s) 0.80V
0.5 Br2 (l) + electron --> Br- 1.08V
0.5 Br2 (aq) + electron --> Br- 1.10V
We obviously know that silver will undergo oxidation and release electrons
Now which bromide equation do we choose? It all depends on the question, look at the states of Br(...) in the given galvanic cell notation thing