8/
$n_{Fe}=30,24/56=0,54mol$
$Fe_3O_4+4H_2\overset{t^o}\to 3Fe+4H_2O$
$\text{Theo pt : }$
$n_{Fe_3O_4}=1/3.n_{Fe}=1/3.0,54=0,18mol$
$⇒m_{Fe_3O_4}=0,18.232=41,76g$
9/
$n_{CuO}=20/80=0,25mol$
$CuO+H_2O\overset{t^o}\to Cu+H_2O$
$\text{Theo pt : }$
$n_{Cu}=n_{CuO}=0,25mol$
$⇒m_{Cu}=0,25.64=16g$