The luminosity of a star is directly proportional to its radius squared. Therefore, if the luminosity of the star is 32 times that of the Sun, then the radius of the star would be √32 times that of the Sun. Since the temperature of the star is not relevant to the radius, the ratio of the star's radius to the Sun's radius would be √32, which is approximately 5.66. Therefore, the best answer would be 5.8.