Answer
See the explanation below.
Work Step by Step
Since, the green graph represents a circle whose radius is equal to $b$ of the given equation $\dfrac{x^2}{25}+\dfrac{y^2}{9}=1$. Thus, the equation of a green circle is: $x^2+y^2=9$
Now, the blue graph represents a circle whose radius is equal to $a$ of the given equation $\dfrac{x^2}{25}+\dfrac{y^2}{9}=1$. Thus, the equation of a green circle is: $x^2+y^2=25$
