Answer :
If you add the two equations, you will indeed eliminate x:
[tex]\begin{cases}y=x+10\\y=-x+3\end{cases} \implies y+y = (x+10)+(-x+3) \iff 2y=13 \iff y=\dfrac{13}{2}[/tex]
If you add the two equations, you will indeed eliminate x:
[tex]\begin{cases}y=x+10\\y=-x+3\end{cases} \implies y+y = (x+10)+(-x+3) \iff 2y=13 \iff y=\dfrac{13}{2}[/tex]