8. Let $A=\left\{a_{1}, a_{2}, \cdots, a_{7}\right\}$. Here $a_{i} \in \mathbf{Z}^{\prime}$, and let $n_{A}$ denote the number of triples $(x, y, z)$ such that: $x<y$, $x+y=z, x, y, z \in A$. Then the maximum possible value of $n_{A}$ is $\qquad$.
8. 9 Let $a<b<c<d<e<f<g$. For any three numbers $x<y<z$, calculate how many times the middle number $y$ appears, thus, for $a, b, c, d, e, f, g$ there are at most $0,1,2,3,2,1,0$ times respectively. Constructing $A=\{1,2,3,4,5,6,7\}$ can achieve this.