It seems like the question is asking for a specific measure of the radius of a cylinder, but the options provided do not give any context or additional information about the cylinder itself. Without further information, I can't determine which of the options (15, 2, 4, or 7.5) is the correct radius.
If you have additional details or context regarding the cylinder (such as a volume, height, or surface area), please provide that, and I would be happy to help you solve for the radius if possible.