(12) Given the arithmetic sequence $\left\{a_{n}\right\}$, the sum of the first 15 terms $S_{15}=30$, then $a_{1}+a_{8}+a_{15}=$
$\qquad$ .
(12) 6 Hint: From
$$
S_{15}=30 \Rightarrow a_{1}+7 d=2,
$$

and
$$
a_{1}+a_{8}+a_{15}=3\left(a_{1}+7 d\right)=6 .
$$