cad/cam help

[claustrophobia9]

hey, for an exam in my CAD/CAM (computer aided design(or drafting)/computer aided modeling(or manufacturing) and we have to use the 3d modeling program "i-deas 9" to recreate this speaker: sorry about how small it is, i have to make the one without dials, the only problem is that the entire thing is curves, and im not great at math, how do i find the radius of a section of a circle without knowing the angle/rotation of the section?