$n_X=\frac{8}{M_X}=\frac{8}{M_Y+16}$
$n_Y=\frac{3,6}{M_Y}$
$n_X-n_Y=0,05$
$\frac{8}{M_Y+16}-\frac{3,6}{M_Y}=0,05$
$⇔8M_Y-3,6M_Y-57,6=0,05M_Y(M_Y+16)$
$⇔0,05M_Y^2+0,8M_Y-4,4M_Y+57,6=0$
$⇔0,05M_Y^2-3,6M_Y+57,6=0$
$⇔\left[\begin{array}{}M_Y=24\\M_Y=48\end{array}\right.$
Với $M_Y=24 \text{ (Mg)}$
$⇒M_X=24+16=40 \text{ (Ca)}$
Với $M_Y=48\text{ (Ti)}$
$⇒M_X=48+16=64 \text{ (Cu)}$