$Cu ( s )+ Sn ^{2+}( aq ) \rightarrow Cu ^{2+}( aq )+ Sn ( s )$
$\left( E _{ Sn ^{2+} \mid Sn }^{0}=-0.16\, V , E _{ Cu ^{2+} \mid Cu }^{0}=0.34\, V \right.$ Take $F=96500\, C\, mol ^{-1}$ )
$=-2 \times 96500[(-0.16)-0.34]+ RT \ln \left(\frac{1}{1}\right)$
$=96500 J$
$F{e^2}+ \left( {aq} \right) + A{g^ + }\left( {aq} \right) \to F{e^{3 + }}\left( {aq} \right) + Ag\left( s \right)$
$E_{Ag^+/Ag}^o = xV$, $E_{F{e^{2 + }}/Fe}^o = yV$, $E_{F{e^{3 + }}/Fe}^o = zV$