The total amount would be 19cm. this is because you add 9+4+6.
I think that was right of the Nurse to do so because the person in the accident was exposed to someone whose blood was HIV positive, and so now they might have it too.
I would have consulted with the patient about if it was okay to let the other person know that they could now be infected with HIV and if the HIV positive patient said it was fine I would go back and tell the other patient.
hope that helps :)
