\[a_{3} = 16;\ \ a_{8} = 15:\]
\[\left\{ \begin{matrix} a_{1} + 2d = 16 \\ a_{1} + 7d = 15 \\ \end{matrix} \right.\ ( - )\text{\ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} - 5d = 1\ \ \ \ \ \ \ \ \ \\ a_{1} = 15 - 7d \\ \end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\left\{ \begin{matrix} d = - 0,2\ \ \ \ \ \ \ \ \\ a_{1} = 15 + 1,4 \\ \end{matrix} \right.\ \]
\[a_{1} = 16,4.\]