Question

3x -7y =-21
5x +7y = 21
Me ajuda pfv

Answer 1

$+\underline{\begin{cases}3x-7y=-21\\5x+7y=21\end{cases}}$

$8x=0\rightarrow\,x=0$

$5.0+7y=21\\7y=21\\y=\dfrac{21}{7}=3$

$\mathsf{s=\{0,3\}}$