Answer
$5$ is not a solution of $x+3>8$ because when $5$ is substituted to $x$, the resulting statement is false.
Work Step by Step
$5$ is a solution if it satisfies $x+3>8$.
Substitute $5$ to $x$ to obtain:
$$\begin{align*}
5+3&\stackrel{?}{>}8\\
8&\not >8
\end{align*}$$
Since $5$ does not satisfy the given inequality, then $5$ is NOT a solution of $x+3>8$.
