How to compute the max/min surface area of a donut-shape solid generated by a revolved 2D circle, as the volume of the solid doesn’t change?

A donut shape solid is generated by revolving a circle $ (x-a)^2+y^2=b^2$ around the y-axis. $ a$ is the distance from the center of the hole of the donut to the center of the circle revolved, and $ b$ is the radius of the circle revolved. I’m trying to compute the minimized surface area and the maximized surface area (if the solid has) with the value of $ a$ and $ b$ , while the volume of the solid doesn’t change (which is $ 90\pi^2$ ). Thanks a lot if someone can help me 🙂