Final answer:
The question involves calculating the focal length of a lens-mirror system, but cannot be answered precisely without additional information such as the refractive index of the lens material. The refractive index is essential for determining the combined system's focal length.
Step-by-step explanation:
The question asks for the calculation of the focal length of a system consisting of an equi-convex lens that has been silverised on one surface to form a mirror. This alters the lens into a combination of a lens and a mirror. To calculate the focal length of the system, we would typically use formulas related to the combination of lenses and mirrors.
However, since the radius of curvature is not used directly to find the new focal length and additional information or context is required to provide a detailed solution (e.g., the refractive index of the lens material), we cannot complete this calculation without all the necessary information. Normally, we would need to consider the effect of the silvered surface on the effective focal length by treating the system as a compound lens, but in absence of the complete information this calculation cannot be precisely undertaken.