7. (10 points) On the Immortal Mountain, there are only two legendary divine creatures: the Nine-Headed Bird and the Nine-Tailed Fox; the Nine-Headed Bird has nine heads and one tail, the Nine-Tailed Fox has nine tails and one head. A Nine-Headed Bird notices that the total number of tails of all other divine creatures on the Immortal Mountain, except for itself, is four times the number of heads; a Nine-Tailed Fox notices that the total number of tails of all other divine creatures on the Immortal Mountain, except for itself, is three times the number of heads. Therefore, the total number of Nine-Tailed Foxes on the Immortal Mountain is $\qquad$.

【Solution】Solution: Let the number of nine-tailed foxes on the immortal mountain be $x$, and the number of nine-headed birds be $y$,
$$
\text { then }\left\{\begin{array}{l}
9 x+y-1=[9(y-1)+x] \times 4 \cdots(1) \\
9(x-1)+y=(9 y+x-1) \times 3 \cdots(2)
\end{array}\right.
$$

From (1), we get: $x-7 y+7=0$
From (2), we get: $3 x-13 y-3=0$
Multiplying (4) by 7 and (3) by 13, we get
$$
\begin{array}{l} 
8 x-112=0 \\
8 x-112+112=0+112 \\
8 x=112 \\
8 x \div 8=112 \div 8 \\
x=14
\end{array}
$$

Answer: There are 14 nine-tailed foxes on the immortal mountain.
Therefore, the answer is: 14.