From the free-form linguistic input to the function expression to calculate the spheroidal surface

I need to calculate the surface area of ​​an oblate spheroid. My first step is to obtain the surface equation of the free form input. But I have trouble converting to a WM function and replacing the focus point and the coefficients of the radius of the major axis with my values.

SurfaceData[Entity["Surface", "Spheroid"], "Image"]SurfaceData[Entity["Surface", "Spheroid"], "Surface area"]sphOblated = Simplify[% /. x_String :> ToExpression[a, c]]{a -> Sqrt[2], c -> 1 /%