6. (3 points) As shown in the figure, the sum of 5 identical two-digit numbers $\overline{\mathrm{AB}}$ is a two-digit number $\overline{M B}$, where the same letters represent the same digits, and different letters represent different digits. Then $\overline{\mathrm{AB}}=$ $\qquad$ .
【Analysis】According to the method of vertical calculation for integer addition, we can deduce as follows.
【Solution】According to the problem, from the addition vertical calculation, we get:
In the units place, the last digit of $5 \times B$ is still $B$. From $5 \times 0=0, 5 \times 5=25$, we can get: $B=0$ or $B=5$; Assuming $B=0$, then in the tens place, $5 \times A=M, M$ must be less than 10, only when $A=1$, $5 \times 1=5$, which fits; Therefore, $A=1, B=0$;

From the above deduction, we get:
$$
\begin{array}{r}
10 \\
10 \\
10 \\
10 \\
+10 \\
\hline 50
\end{array}
$$

Assuming $B=5$, $5 \times 5=25$, carry 2 to the tens place;
In the tens place, $5 \times A+2=M, M$ must be less than 10, only when $A=1$, $5 \times 1+2=7$, which fits;
Therefore, $A=1, B=5$;
From the above deduction, we get:
Thus, the two-digit number $\overline{\mathrm{AB}}$ is: 10 or 15.
The answer is: 10 or 15.