What is a cell constant?

What is standard cell potential for the reaction

$3\mathrm{Ni}\left(\mathrm{s}\right)+2{\mathrm{Al}}^{3\oplus }\left(1\mathrm{M}\right)⟶3{\mathrm{Ni}}^{2\oplus }\left(1\mathrm{M}\right)+2\mathrm{Al}\left(\mathrm{s}\right)$ if ${\mathrm{E}}_{\mathrm{Ni}}^0=-0.25 \mathrm{V}$ and ${\mathrm{E}}_{\mathrm{Al}}^0=-1.66 \mathrm{V}$?

Formulate a cell from the following electrode reactions:

${\mathrm{Au}}^{3\oplus }\left(\mathrm{aq}\right)+3{\mathrm{e}}^{\ominus }⟶\mathrm{Au}\left(\mathrm{s}\right)$

$\mathrm{Mg}\left(\mathrm{s}\right)⟶{\mathrm{Mg}}^{2\oplus }\left(\mathrm{aq}\right)+2{\mathrm{e}}^{\ominus }$