We don't know anything about the x coordinate of point B other than it cannot be zero (which is what the slash through the equal sign means). You can pick any value you want for x as long as it's not zero. So I'm going to pick x = 1. Point B is located at (x,y) = (1,-7)
Find the slope of the line through A(-5,5) and B(1,-7). Use the slope formula
m = (y2 - y1)/(x2 - x1)
m = (-7-5)/(1 - (-5))
m = (-7-5)/(1 + 5)
m = (-12)/(6)
m = -2
Use this slope value with (x,y) = (-5,5) to find the y intercept b
y = mx+b
y = -2x + b
5 = -2(-5) + b
5 = 10 + b
5-10 = 10+b-10
-5 = b
b = -5
So y = mx+b turns into y = -2x-5 which is the equation of the line through the two points A(-5,5) and B(1,7). The graph is shown below.
note: this answer will be different if you pick a different x coordinate for point B