Electrochemistry

For the cell reaction, $\mathrm{A}_{(\mathrm{s})}+\mathrm{B}_{(\mathrm{eq})}^{+_2} \longrightarrow \mathrm{~A}_{(\mathrm{eq})}^{+_2}+\mathrm{B}_{(\mathrm{s})}$ if equilibrium constant of reaction is $10^4$ at 298 K . What is standard emf of cell?