5. (8 points) Given: $1 \times 9+2=11,12 \times 9+3=111,123 \times 9+4=1111, \cdots, \triangle \times 9+O=111111$, then $\triangle+O=$ . $\qquad$
5. (8 points) Given: $1 \times 9+2=11,12 \times 9+3=111,123 \times 9+4=1111, \cdots, \triangle \times 9+O=111111$, then $\triangle+O=12351$.
【Solution】Solution: From the given, $1 \times 9+2=11,12 \times 9+3=111,123 \times 9+4=1111,1234 \times 9+5=11111$, $12345 \times 9+6=111111$,
so $\triangle=12345, \bigcirc=6$,
thus $\triangle+O=12345+6=12351$,
hence the answer is 12351.