Respuesta :

first find the slope m of the line:
m=(y2-y1)/(x2-x1)
=(3-5)/(1-(-1))
=-2/2=-1

now you know y=-1x+b
to calculate b insert x and y of any point, like (-1,5):
y=-1x+b
5=-1*-1+b
5=1+b
4=b

-> y=-1x+4
x+y=4

which matches B. X+y=4

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