A metallic wire of uniform area of cross section has a resistance R, resistivity ρ and power rating P at V volts. The wire is uniformly stretched to reduce the radius to half the original radius. The values of resistance, resistivity and power rating at V volts are now denoted by R', ρ' and P' respectively. The corresponding values are correctly related as ___________.
Fill in the blank with the correct answer from the options given below.