Next time you share two equations, write one equation per line, or separate the two equations with a comma, OK?
y=−x+2y=4x+7 NO
y=−x+2 YES
y=4x+7
Multiply the first equation by 4, obtaining: 4y = -4x + 8
Add the 2nd equation to this result: y = 4x + 7
--------------------
5y = 15, and y = 3
Then, using the first equation, determine x:
y = 3 = -x + 2
1 = -x, so x = -1
The solution is (-1, 3)