Redox Reactions

If the number of moles of $\mathrm{Fe}^{2+}$ ions oxidised by one mole of acidified $\mathrm{MnO}_4^{-}$is $x$, the number of moles of $\mathrm{Fe}^{2+}$ ions oxidised by one mole of acidified $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is