Cameras are not like binoculars, where 8x or 10x actually means something. The 26x does not necessarily have "5x more zoom" than the 21x, it may even have less total magnification. What you need to know is the focal lengths of the lenses. The 21x and 26x just denotes the magnitude of difference between the nearest and farthest focal lengths of the zoom range.
For example, a zoom lens that covers a focal length range from 10mm to 100mm is a "10x zoom" (its maximum focal length is 10 times its shortest).
A lens that covers from 50mm to 100mm is a "2x zoom".
Both lenses have exactly the same maximum magnification, although the 10-100mm is obviously capable of shooting a much wider angle shot. And if you had a lens that covered from 50mm to 200mm it would be a 4x zoom, but would have double the magnification ability of either of the 100mm lenses.
Calling lenses 20x, 25x, etc., is just marketing spin.