It looks like you're asking about possible values for the radius of the base of a cylinder. However, there is no specific context or information given about the cylinder, such as its volume or height, to reason from.
If you can provide more details or a specific problem involving the cylinder, I can help you determine or choose the correct radius. Otherwise, you have the options of 2, 4, 15, and 7.5, and without more information, any of these could potentially be the radius.