In the equation :

${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-} + {\mathrm{Fe}}^{2+} + {\mathrm{H}}^{+} \to {\mathrm{Cr}}^{3+} + {\mathrm{Fe}}^{3+} + {\mathrm{H}}_2\mathrm{O}$

the coefficients of ${\mathrm{Fe}}^{2+} \mathrm{and} {\mathrm{H}}^{+}$ are respectively

${\stackrel{+6}{\mathrm{Cr}}}_2{\mathrm{O}}_7^{-2}+ {\mathrm{Fe}}^{+2}+{\mathrm{H}}^{+}\to 2{\mathrm{Cr}}^{+3}+{\mathrm{Fe}}^{+3}+{\mathrm{H}}_2\mathrm{O}$

By cross multiply the change in oxidation states,

${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-} + 6{\mathrm{Fe}}^{2+} + 14{\mathrm{H}}^{+} \to 2{\mathrm{Cr}}^{3+} + 6{\mathrm{Fe}}^{3+} + 7{\mathrm{H}}_2\mathrm{O}$