\[\boxed{\text{605}\text{\ (605)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[S_{n} = \frac{2b_{1} + d(n - 1)}{2} \cdot n\]
\[\textbf{а)}\ b_{1} = - 17;\ \ d = 6:\]
\[S_{9} = \frac{2 \cdot ( - 17) + 6 \cdot 8}{2} \cdot 9 = \frac{48 - 34}{2} \cdot 9 = 63.\]
\[\textbf{б)}\ b_{1} = 6,4;\ \ \ d = 0,8:\]
\[S_{n} = \frac{2 \cdot 6,4 + 0,8 \cdot 8}{2} \cdot 9 = (6,4 + 3,2) \cdot 9 = 86,4.\]