[tex]\left\{\begin{matrix}
3a + 5c = 27\\
3a + 3c = 18 \: | \times ( - 1)\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}
3a + 5c = 27\\
- 3a - 3c = - 18\end{matrix}\right.[/tex]
[tex]3a - 3a + 5c - 3c = 27 - 18[/tex]
[tex]2c = 9[/tex]
[tex]c = \frac{9}{2} [/tex]
[tex]c = 4.5 \: lei[/tex]
[tex]3a + 5c = 27[/tex]
[tex]3a + 5 \times 4.5 = 27[/tex]
[tex]3a + 22.5 = 27[/tex]
[tex]3a = 27 - 22.5[/tex]
[tex]3a = 4.5[/tex]
[tex]a = \frac{4.5}{3} [/tex]
[tex]a = 1.5 \: lei[/tex]
