\[\boxed{\mathbf{863\ (863)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\textbf{а)}\ 15\ \in N;\ \ 15 \in Z;\ \ 15 \in Q\]
\[\textbf{б)} - 30\ \in Z;\ - 30 \in Q\]
\[\textbf{в)}\ 2,5\ \in Q\]
\[\textbf{г)} - 12,5\ \in Q.\]