The reaction $R$ of the body to a dose $Q$ of medication is often represented by the general function $$R(Q)=Q^{2}\left(\frac{k}{2}-\frac{Q}{3}\right)$$
where $k$ is a constant and $R$ is in millimeters of mercury $(\mathrm{mmHg})$ if the reaction is a change in blood pressure or in degrees Fahrenheit $\left(^{\circ} \mathrm{F}\right)$ if the reaction is a change in temperature. The rate of change $d R / d Q$ is defined to be the body's sensitivity to the medication.
a) Find a formula for the sensitivity.
b) Explain the meaning of your answer to part (a).