18. (8 分)计算.
(1) $(-3)^{2}+(-2)^{3}×(-\frac {1}{4})÷(-\frac {1}{2})$;
(2) $-1^{2}-(\frac {7}{8}+\frac {7}{12}-\frac {5}{6})×(-24)$.

(1) 原式$=9 + (-8)×(-\frac{1}{4})×(-2)$
$=9 + 2×(-2)$
$=9 - 4$
$=5$
(2) 原式$=-1 - [\frac{7}{8}×(-24) + \frac{7}{12}×(-24) - \frac{5}{6}×(-24)]$
$=-1 - [(-21) + (-14) + 20]$
$=-1 - (-15)$
$=-1 + 15$
$=14$