Which vial of heparin sodium is most appropriate to use

Question

Question: The MD changes the dose of the patient's heparin to: Heparin Sodium Injection 8,000 units SUBQ every 12 hr. The nurse prepares the heparin and finds the following vials of heparin in the patient's medication cart: Multidose vial of Heparin Sodium Injection USP 1,000 units per mL Multidose vial of Heparin Sodium Injection USP 20,000 units per mL Which vial of heparin sodium is most appropriate to use? How many mL will the nurse administer?