1. A patient takes medication at midday. The amount of a certain drug in their bloodstream, $D$ mg, $h$ hours after midday is modelled by the equation

$D=0.06+0.21h-a{h}^{2}$

where $a$ is a positive constant and $0\leqh\leq6$.

Write down the value of $D(0)$ and interpret what this value represents in the context of the model.