Question

A nurse practitioner prepares an injection of promethazine, an antihistamine used to treat allergic rhinitis. If the stock bottle is labeled 30. mg/mL and the order is a dose of 15.0 mg , how many milliliters will the nurse draw up in the syringe?

Answer 1

Essentially what the question is asking you to find is the volume of promethazine the nurse will fill the syringe with.  The question gives you :
-  Density =  30 mg / mL
-  Mass    =  15.0 mg

Therefore you can solve using the formula:
    $Volume = \frac{mass}{density}$
                   =   $\frac{15 mg}{30 mg / L}$
                   =    0.5 mL