$(A)$ $\left. Na _{4}\left[ Fe ( CN )_{5} NOS \right)\right]$
$(B)$ $Na _{4}\left[ FeO _{4}\right]$
$(C)$ $\left[ Fe _{2}( CO )_{9}\right]$
$(+1) 4+x+(-1) 5+(-1) 1=0$
$x=+2$
$\left( B \right)\,N{a_4}\left[ {\mathop {Fe{O_4}}\limits^y } \right]$
$(+1) 4+y+(-2) 4=0$
$y=+4$
$\left( C \right)\,\left[ {F\mathop {{e_2}}\limits^z {{\left( {CO} \right)}_9}} \right]$
$2 z+0 \times 9=0$
$z=0$
so $( x + y + z )=+2+4+0$
$=6$