Answer
$$
f(x)=18x-18e^{-x}
$$
$f(x)$ is never concave upward
$f(x)$ always concave downward
No Inflection points.
Work Step by Step
$$
f(x)=18x-18e^{-x}
$$
The first derivative is
$$
\begin{aligned}
f^{\prime}(x) &=18-(-1)18e^{-x}\\
&=18+18e^{-x} ,
\end{aligned}
$$
and the second derivative is
$$
\begin{aligned}
f^{\prime\prime}(x) &=0+18(-1)e^{-x} ,\\
&=-18e^{-x}
\end{aligned}
$$
Since
$$
\begin{aligned}
f^{\prime\prime}(x) &=-18e^{-x} \lt 0
\end{aligned}
$$
for all $x$, so function $f$ is always concave downward and never concave upward and also there are no points of inflection .
