I think you missed attaching the picture, so hope my photo fits your questions well!
We must consider the median of the data sets, it may represent the center of the dispersion measure. Then we see answer C is the most suitable one, this is because it's median is approximately to $60.
Each cylindrical shell has radius (the horizontal distance from the axis of revolution to the curve ); has height (the vertical distance between a point on the -axis in and the curve ).