$a)C_6H_5-C_2H_5\rightarrow C_6H_5-CH=CH_2+H_2$ $106 104$
$\Rightarrow m_{LT}=\frac{66,25.104}{106}\Rightarrow H_1=\frac{52.106.100}{66,25.104}=80\%$
$b)n_{stiren du}=n_{Br_2}=0,009 mol\Rightarrow n_{stiren pu}=\frac{5,2}{104}-0,009=0,041 mol$
$\Rightarrow H_2=\frac{0,041.100}{0,05}=82\%\Rightarrow m=52.H_2=42,64 Kg$