Answer
See below
Work Step by Step
We know the following equation for an ellipse centered at the origin:
$$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$$
Where $(\pm a,0)$ is the vertex and $(0,\pm b)$ is the co-vertex.
Thus, we find:
$$\frac{x^2}{(5)^2}+\frac{y^2}{(4)^2}=1$$
$$\frac{x^2}{25}+\frac{y^2}{16}=1$$