$\begin{aligned}
& \mathrm{e}_1^2=1-\frac{\mathrm{b}^2}{25} \quad \mathrm{e}_2^2=1-\frac{\mathrm{b}^2}{16} \
& \therefore \mathrm{e}_1^2 \mathrm{e}_2^2=1 \
& \left(1-\frac{\mathrm{b}^2}{25}\right)\left(1+\frac{\mathrm{b}^2}{16}\right)=1 \
& \Rightarrow 2+\frac{\mathrm{b}^2}{16}-\frac{\mathrm{b}^2}{25}-\frac{\mathrm{b}^2}{400}=1 \
& \Rightarrow \frac{9 \mathrm{b}^2}{400}=\frac{\mathrm{b}^4}{400} \
& \mathrm{b}^2=9 \
& \frac{\mathrm{x}^2}{9}+\frac{\mathrm{y}^2}{25}=1 \quad \frac{\mathrm{x}^2}{16}-\frac{\mathrm{y}^2}{9}=0 \
& \mathrm{e}_1 \sqrt{1-\frac{9}{25}} \
& \mathrm{e}_1=\frac{4}{5}
\end{aligned}$
Focii : - (0,±4)(±5,0)
ellipse passing through all four foci
$\begin{aligned}
& \frac{x^2}{25}+\frac{y^2}{16}=1 \
& e=\sqrt{1-\frac{16}{25}}=\frac{3}{5}
\end{aligned}$