If complex compound, $\left[\mathrm{Fe}{\left(\mathrm{\pi }-{\mathrm{C}}_5{\mathrm{H}}_5\right)}_{\mathrm{x}}{\left(\mathrm{\pi }-{\mathrm{C}}_3{\mathrm{H}}_5\right)}_{\mathrm{y}}(\mathrm{CO}{)}_{\mathrm{z}}\right]$ is following the Sidwick's rule of EAN then value of expression " x + y + z" is :
(Where x,y and z are natural numbers)

$\text{ Ligand (s) }$                                        $\text{ One ligand donate }2{\mathrm{e}}^{-}$
$\mathrm{\pi }-{\mathrm{C}}_5{\mathrm{H}}_5$                                           $6{\mathrm{e}}^{-}$
$\mathrm{\pi }-{\mathrm{C}}_3{\mathrm{H}}_5$                                           $4{\mathrm{e}}^{-}$
$\mathrm{CO}$                                                     $2{\mathrm{e}}^{-}$
$\text{ If }\left[\mathrm{Fe}{\left(\mathrm{\pi }-{\mathrm{C}}_5{\mathrm{H}}_5\right)}_{\mathrm{x}}{\left(\mathrm{\pi }-{\mathrm{C}}_3{\mathrm{H}}_5\right)}_{\mathrm{y}}(\mathrm{CO}{)}_2\right]$
Complex compound following Sidewick's rule then
26 -(2) +6 (1) + 4 (1) +2 (1) = 36
x+y+z =1+1+1 =3