$a)+\{\begin{array}{l}x+y=6\\ x-y=2\end{array}$  

$\underline{}$    

$x+x+y-y=6+2$  

$2x=8\mid :2$  

$x=4$  

 

$\{\begin{array}{l}x=4\\ x-y=2\end{array}$  

$\{\begin{array}{l}x=4\\ 4-y=2\mid -4\end{array}$  

$\{\begin{array}{l}x=4\\ -y=-2\mid \cdot \left(-1\right)\end{array}$ $\{\begin{array}{l}x=4\\ -y=-2\mid \cdot \left(-1\right)\end{array}$  

$\{\begin{array}{l}x=4\\ y=2\end{array}$  

$b)+\{\begin{array}{l}4x+y=5\\ 2x-y=-2\end{array}$  

$\underline{}$  

$4x+2x+y-y=5-2$  

$6x=3\mid :6$  

$x=\frac{3}{6}=\frac{1}{2}$  

$\{\begin{array}{l}x=\frac{1}{2}\\ 4x+y=5\end{array}$  

$\{\begin{array}{l}x=\frac{1}{2}\\ 4\cdot \frac{1}{2}+y=5\end{array}$  

$\{\begin{array}{l}x=\frac{1}{2}\\ 2+y=5\mid -2\end{array}$  

$\{\begin{array}{l}x=\frac{1}{2}\\ y=3\end{array}$  

$c)+\{\begin{array}{l}2x+3y=5\\ -2x+y=-1\end{array}$  

  $\underline{}$  

  $2x-2x+3y+y=5-1$  

$4y=4\mid :4$  

$y=1$  

$\{\begin{array}{l}y=1\\ -2x+1=-1\mid -1\end{array}$  

$\{\begin{array}{l}y=1\\ -2x=-2\mid :\left(-2\right)\end{array}$  

$\{\begin{array}{l}y=1\\ x=1\end{array}$  

$d)+\{\begin{array}{l}3x+2y=21\\ -3x+y=-30\end{array}$  

$\underline{}$  

$3x-3x+2y+y=21-30$  

$3y=-9\mid :3$  

$y=-3$  

$\{\begin{array}{l}y=-3\\ 3x+2y=21\end{array}$  

$\{\begin{array}{l}y=-3\\ 3x+2\cdot \left(-3\right)=21\end{array}$  

$\{\begin{array}{l}y=-3\\ 3x-6=21\mid +6\end{array}$  

$\{\begin{array}{l}y=-3\\ 3x=27\mid :3\end{array}$  

$\{\begin{array}{l}y=-3\\ x=9\end{array}$