y = -x + 5
Slope of this line = - 1.
Slope of the line that is perpendicular is negative reciprocal.
For example if slope= a/b, then slope of the perpendicular line = -b/a.
For our line, the slope is going to be -(-1)=1.
y=mx +b
m=1
y=x+b
We need to find b. We are going to use point (5, -1).
y = x +b
-1 = 5 + b
b= -6
So,
y= x - 6
Answer is A.