The acidity of a solution is measured by its pH value, which is defined by pH = −log₁₀ [H₃O⁺], where [H₃O⁺] is the hydronium ion concentration (moles/liter) of the solution. On average, milk has a pH value that is three times the pH value of a lime, which in turn has half the pH value of an orange. If the average pH of an orange is 3.2, what is the average hydronium ion concentration of a lime?