6. (4 points) The students form a square array for the radio calisthenics performance. Xiao Hai's position is the 5th from the front, from the back, from the left, and from the right. The total number of students participating in the radio calisthenics performance is $\qquad$ people.
【Answer】Solution: According to the analysis of the problem, we get:
$$
\begin{array}{l}
5+5-1=9 \text { (people) } \\
9 \times 9=81 \text { (people) }
\end{array}
$$

Answer: A total of 81 people participated in the radio calisthenics performance. Therefore, the answer is: 81.