[tex]\left\{\begin{matrix}
i + p = 10 \: | \times ( - 2)\\
4i + 2p = 34\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
- 2i - 2p = - 20\\
4i + 2p = 34\end{matrix}\right.[/tex]
[tex] - 2i + 4i - 2p + 2p = - 20 + 34[/tex]
[tex]2i = 14 \: | \div 2[/tex]
[tex]i = 7[/tex]
[tex]i + p = 10[/tex]
[tex]7 + p = 10[/tex]
[tex]p = 10 - 7[/tex]
[tex]p = 3[/tex]