15. (6 points) The students of Class 3 (1) are lined up in three rows for morning exercises, with an equal number of students in each row. Xiao Hong is in the middle row. Counting from left to right, she is the 6th; counting from right to left, she is the 7th. The total number of students in the class is $\qquad$.
15. (6 points) The students of Class 3 (1) are lined up in three rows for morning exercises, with an equal number of students in each row. Xiao Hong is in the middle row. Counting from left to right, she is the 6th; counting from right to left, she is the 7th, and there are 36 students in total.
【Solution】Solution: $(6+7-1) \times 3$,
$$
\begin{array}{l}
=12 \times 3, \\
=36 \text { (people); }
\end{array}
$$

Answer: There are 36 students in total.
Therefore, the answer is: 36.