Given, standard electrode potentials of following reactions,
$Fe ^{2+}+2 e^{-} \longrightarrow Fe ; E^{\circ}=-0.440\, V $
$Fe ^{3+}+3 e^{-} \longrightarrow Fe ; E^{\circ}=-0.036\, V$
The standard electrode potential $\left(E^{\circ}\right)$ for
$Fe ^{3+}+e^{-} \longrightarrow Fe ^{2+}$, is