Given, ${\mathrm{E}}_{{\mathrm{I}}_2/{\mathrm{I}}^{-}}^{\mathrm{o}}(1 \mathrm{M})=+0.54 \mathrm{V}, \mathrm{and} {\mathrm{E}}_{{\mathrm{Br}}_2/{\mathrm{Br}}^{-}}^{\mathrm{o}}(1 \mathrm{M})=1.09 \mathrm{V}$ On this basis the feasible reaction is

$2{\mathrm{I}}^{-}\to {\mathrm{I}}_2+2{\mathrm{e}}^{-}\left(\mathrm{oxidation}\right)$
$\frac{{\mathrm{Br}}_2+2{\mathrm{e}}^{-}\to 2{\mathrm{Br}}^{-}\left(\mathrm{reduction}\right)}{2{\mathrm{I}}^{-}+{\mathrm{Br}}_2\to {\mathrm{I}}_2+2{\mathrm{Br}}^{-}\left(\mathrm{net} \mathrm{reduction}\right)}$
${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}=1.09-0.54=+0.55 \mathrm{V}$
Positive ${\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}}$ means reaction is feasible.