Two fully annealed cylindrical specimens of an alloy are to be hardened by reducing their (always circular) cross-sections in an extrusion process. For one specimen, the initial and post-deformation radii are 15mm and 12 mm, respectively. The second specimen has an initial radius of 11 mm, and is required to end up with the same hardness as the first specimen when both have been deformed.
Calculate the post-deformation radius of the second specimen.