A fish swims at a speed v relative to the water, against a current of 3 mi/h. Using a mathematical model of energy expenditure, it can be shown that the total energy E required to swim a distance of 6 mi is given by E(v) = 2.73v3 6 v − 3 . Biologists believe that migrating fish try to minimize the total energy required to swim a fixed distance. Find the value of v that minimizes energy required.