What is the intersection coordinate (m, 2) of the image of the first-order function y = - x + A and the first-order function y = x + B

What is the intersection coordinate (m, 2) of the image of the first-order function y = - x + A and the first-order function y = x + B

Hello
a+b=4
y=-x+a,y=x+b
The sum of the two formulas leads to
2y=a+b
y=2
4=a+b
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