Answer
$\frac{x^2}{25}+\frac{y^2}{9}=1$
Work Step by Step
$(0,±b)=(0,±3)$
$b=3$
The major axis is horizontal.
Foci: $(±c,0)$. So, the distance between foci is $c-(-c)=2c$
$2c=8$
$c=4$
$a^2=b^2+c^2=3^2+4^2=9+16=25$
$a=5$
Equation of the ellipse:
$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$
$\frac{x^2}{5^2}+\frac{y^2}{3^2}=1$
$\frac{x^2}{25}+\frac{y^2}{9}=1$