Answer
Concave up
Work Step by Step
The rate of change between $x=12$ and $x=15$ is
$$
\frac{\Delta H(x)}{\Delta x}=\frac{21.53-21.40}{15-12} \approx 0.043
$$
Similarly, we have
$$
\begin{aligned}
& \frac{\Delta H(x)}{\Delta x}=\frac{21.75-21.53}{18-15} \approx 0.073 \\
& \frac{\Delta H(x)}{\Delta x}=\frac{22.02-21.75}{21-18} \approx 0.090 .
\end{aligned}
$$
The rate of change is increasing, so we expect the graph of $H(x)$ to be concave up.
