Flow of a polyisoprene solution in a pipe, a 13.5% (by weight) solution of polyisoprene in isopentane has the following power law parameters at 323 K: n = 0.2 and m = 5 x 10³ Pa ∙ sⁿ. It is being pumped (in laminar flow) through a horizontal pipe that has a length of 10.2 m and an internal diameter of 1.3 cm. It is desired to use another pipe with a length of 30.6 m with the same mass flow rate and the same pressure drop. What should the pipe radius be?