One hour after $x$ milligrams of a drug are given to a person, the change in body temperature $T(x)$ (in degrees fahrenheit) is given by the function $$T(x) = x^2 (1 - \frac{x}{4}).$$ Further, the rate $T'(x)$ at which $T$ changes with respect to the size of the dosage, $x$, is called the sensitivity of the body to the dosage. Find:
(A) $T'(1)$ =
(B) $T'(3)$ =
(C) $T'(6)$ =