Answer
$\left\{6, 9\right\}$.
Work Step by Step
The subsets of $\left\{6, 9\right\}$ are:
$\left\{\right\}
\\\left\{6\right\}
\\\left\{9\right\}
\\\left\{6, 9\right\}
\\$
RECALL:
$A$ is a proper subset of $B$ if all elements of $A$ are in $B$, but $B$ has at least one element that is no in $A$.
Thus, among the subsets of $\left\{6, 9\right\}$, the proper subsets are:
$\left\{\right\}
\\\left\{6\right\}
\\\left\{9\right\}$
The only non-proper subset is $\left\{6, 9\right\}$.
