$\text{a)}$  

$\{\begin{array}{l}x-y=1\\ x+y=3\end{array}$  

$2x=4$  

$x=2$  

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$\text{b)}$     

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

$3x=6$  

$x=2$  

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$\text{c)}$  

$\{\begin{array}{l}-x+3y=0\\ 2x-3y=7\end{array}$  

$x=7$  

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$\text{d)}$  

$\{\begin{array}{l}-4x+2y=-1\\ 2x-2y=3\end{array}$  

$-2x=2$  

$x=-1$