When does a cell reaction occur spontaneously?

The $E^o$ values of $Mg^{2+}/Mg$ is $-2.37 \ V$,$Zn^{2+}/Zn$ is $-0.76 \ V$,and $Fe^{2+}/Fe$ is $-0.44 \ V$. Which of the following statements is correct?

The standard reduction potentials for two half-cell reactions are given below:
$Cd^{2+}_{(aq)} + 2e^{-} \rightarrow Cd_{(s)}, E^o = -0.40 \ V$
$Ag^{+}_{(aq)} + e^{-} \rightarrow Ag_{(s)}, E^o = 0.80 \ V$
What is the standard free energy change $\Delta G^o$ in $kJ$ for the reaction $2Ag^{+}_{(aq)} + Cd_{(s)} \rightarrow 2Ag_{(s)} + Cd^{2+}_{(aq)}$?

On the basis of the following $E^o$ values,the strongest oxidizing agent is:
$[Fe(CN)_6]^{4-} \to [Fe(CN)_6]^{3-} + e^-; E^o = -0.35 \ V$
$Fe^{2+} \to Fe^{3+} + e^-; E^o = -0.77 \ V$

Discuss the method to determine the cell potential of any cell when a standard hydrogen electrode is considered as the anode,with a suitable example.

Calculate the standard cell potential (in $V$) of the cell in which the following reaction takes place:
$Fe^{2+}_{(aq)} + Ag^{+}_{(aq)} \to Fe^{3+}_{(aq)} + Ag_{(s)}$
Given that:
$E^o_{Ag^{+}/Ag} = x \ V$
$E^o_{Fe^{2+}/Fe} = y \ V$
$E^o_{Fe^{3+}/Fe} = z \ V$