(7) In a regular tetrahedron \(ABCD\) with edge length 1 meter, a small insect starts crawling from vertex \(A\) according to the following rules: at each vertex, it chooses one of the three edges connected to that vertex with equal probability and crawls all the way to the end of the edge. Let \(P_n\) be the probability that the insect returns to point \(A\) after crawling \(n\) meters. Then \(P_4=\)
(7) $\frac{7}{27}$