The physician orders Decadron

A 64-Ib child has a severe allergic reaction to a bee sting. The physician orders Decadron. The normal adult dose is Decadron 4 mg. The available medication is dexamethasone elixir 0.5 mg/5 mL. What rule is needed for this calculation? What strength of medication should be administered to the child? What volume of medication should be administered to the child?