\[\boxed{\text{987\ (987).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[a_{6} = - 6,\ \ a_{16} = 17,5,\ \ \]
\[S_{16} = ?\]
\[S_{16} = \frac{a_{1} + a_{16}}{2} \cdot 16 =\]
\[= 8 \cdot ( - 17,75 + 17,5) = - 2.\]