A drug is injected into the bloodstream of a patient through

A drug is injected into the bloodstream of a patient through her left arm. The concentration of the drug (in milligrams per cubic centimeter) in her right arm t hours after the injection is given is given by C(t) = 0.12t / (t2 + 1)

What is the instantaneous rate of change of the concentration of the drug in her right arm 3 hours after the drug is injected into her left arm?