here is a problem im not sure how to start...

the region bounded by y = r ^2 minus x^2, y=0, and x=0 is revolved about the y-axis to form a paraboloid. a hole, centered along the x-axis of revolution, is drilled through this solid. the hole has a radius k, 0< k< r. find the volume of the resulting ring (a) by integrating with respect to x and (b) by integrating with respect to y.

im not sure where to start on this one. maybe this parabola is facing down with a rel max at (0,r)? so i would take the volume of the parabola and subtract it from the volume of the ring? or would it create a sphere since it is being rotated? im a little confused on this one....any help would be appreciated. thanks in advance.