a,
$Mg+H_2SO_4\to MgSO_4+H_2$
$Zn+H_2SO_4\to ZnSO_4+H_2$
b,
Gọi a, b là mol Mg, Zn.
$\Rightarrow 24a+65b=15,4$ (1)
$n_{H_2}=\frac{6,72}{22,4}=0,3 mol$
$\Rightarrow a+b=0,3$ (2)
(1)(2) $\Rightarrow a=0,1; b=0,2$
$\%m_{Mg}=\frac{0,1.24.100}{15,4}= 15,58\%$
$\%m_{Zn}= 84,42\%$