解:
$\begin{aligned}&\frac{1}{105}\div[\frac{1}{7}-(-\frac{1}{3})-\frac{1}{5}]×(-87)\\=&\frac{1}{105}\div(\frac{1}{7}+\frac{1}{3}-\frac{1}{5})×(-87)\\=&\frac{1}{105}\div(\frac{15 + 35 - 21}{105})×(-87)\\=&\frac{1}{105}\div\frac{29}{105}×(-87)\\=&\frac{1}{105}×\frac{105}{29}×(-87)\\=&\frac{1}{29}×(-87)\\=& - 3\end{aligned}$