If $a$ and $b$ are digits for which:

\[
\begin{array}{ccc}
  & 2 & a \\
\times & b & 3 \\
\hline
  & 6 & 9 \\
9 & 2 \\
\hline
9 & 8 & 9
\end{array}
\]

Find the value of $a + b$.

Let's think step by step and output the final answer within \boxed{}.
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