JEE Main 2022 · 29 Jun · Shift 2, Mathematics question 25

For real numbers $a,b$ $(a>b>0)$, let
$$\text{Area}\left\{(x,y):x^2+y^2\le a^2\text{ and }\frac{x^2}{a^2}+\frac{y^2}{b^2}\ge1\right\}=30\pi$$
and
$$\text{Area}\left\{(x,y):x^2+y^2\ge b^2\text{ and }\frac{x^2}{a^2}+\frac{y^2}{b^2}\le1\right\}=18\pi$$
Then the value of $(a-b)^2$ is equal to ______.