$n_{Zn}=\dfrac{6,5}{65}=0,1 mol$
$Zn+2HCl\to ZnCl_2+H_2$
$\Rightarrow n_{HCl}=0,1.2=0,2 mol$
$\Rightarrow m_{dd HCl}=0,2.36,5:12\%=\dfrac{365}{6}g$
$n_{ZnCl_2}=n_{H_2}=0,1 mol$
$\Rightarrow m_{dd\text{spu}}=6,5+\dfrac{365}{6}-0,1.2=\dfrac{1007}{15}g$
$\to C\%_{ZnCl_2}=\dfrac{0,1.136.100}{\frac{1007}{15}}=20,3\%$