Пожалуйста помогите решить способом слажения 1) 2) и 3) даю 20 балов

[latex]\left\{\begin{matrix} u &+ &v &= &4&|\cdot3\\ 3u &- &5v &= &20 \end{matrix}\right.\\\\\\ \left\{\begin{matrix} 3u &+ &3v &= &12\\ 3u &- &5v &= &20 \end{matrix}\right.\\\\\\ 8v=-8\\ v=-1\\\\ u-1=4\\ u=5[/latex] Ответ: [latex](5;-1)[/latex] [latex] \left\{\begin{matrix} 2x &+ &3y &= &-1&|\cdot5\\ 3x &+ &5y &= &-2&|\cdot3 \end{matrix}\right.\\\\\\ \left\{\begin{matrix} 10x &+ &15y &= &-5\\ 9x &+ &15y &= &-6 \end{matrix}\right.\\\\\\ x=1\\\\ 3+5y=-2\\ 5y=-5\\ y=-1[/latex] Ответ: [latex](1;-1)[/latex] [latex]\left\{\begin{matrix} \frac{3a+1}{5} &+ &\frac{2b-1}{3} &= &\frac{2}{5} \\ \\ \frac{3a-2}{2} &+ &\frac{b-3}{4} &= &1 \end{matrix}\right.\\\\\\ \left\{\begin{matrix} \frac{9a+10b-2}{15}&= &\frac{2}{5}&|\cdot5 \\\\ \frac{6a+b-7}{4}&= &1 &|\cdot4 \end{matrix}\right.\\\\\\ \left\{\begin{matrix} \frac{9a+10b-2}{3}&= &2 \\ \\ 6a+b-7 &= &4 \end{matrix}\right.\\\\\\ \left\{\begin{matrix} 9a &+ &10b &= &8&|\cdot2 \\ 6a &+ &b &= &11 &|\cdot3 \end{matrix}\right.[/latex] [latex]\left\{\begin{matrix} 18a &+ &20b &= &16 \\ 18a &+ &3b &= &33 \end{matrix}\right.\\\\\\ 17b=-17\\ b=-1\\\\ 6a-1=11\\ 6a=12\\ a=2 [/latex] Ответ: [latex](-1;2)[/latex]