See the following chemical reaction: Cr_2 O_7^2-+ X H^++6 F_e^2+ → YCr^3++6 F_e^3++ ZH_2 O The sum of X, Y and Z is ____

See the following chemical reaction: $$\mathrm{Cr}_2 \mathrm{O}_7^{2-}+\mathrm{X} \mathrm{H}^{+}+6 \mathrm{~F}_e^{2+} \rightarrow \mathrm{YCr}^{3+}+6 \mathrm{~F}_e^{3+}+\mathrm{ZH}_2 \mathrm{O} $$ The sum of $\displaystyle \mathrm{X}, \mathrm{Y}$ and Z is $\displaystyle \_\_\_\_$