3. Let $\left\{a_{n}\right\}$ be a geometric sequence with real terms, the sum of the first $k$ terms is $S_{k}$, and the common ratio $q$ satisfies $|q| \neq 1$. If $S_{6 n}=$ $2 S_{4 n}+11 S_{2 n}$, then $\frac{S_{10 n}}{S_{8 n}}=$ $\qquad$