7.
The point-slope form of the equation of a line is
y - y1 = m(x - x1)
where m is the slope, and (x1, y1) is a point on the line.
We are given two points, so we can find the slope.
slope = m = (y2 - y1)/(x2 - x1)
The slope of this line is
m = (-3 - 7)/(5 - (-15)) = -10/20 = -1/2
Since every choice has a 7 and a 15, we now use point (-15, 7) and slope -1/2.
y - y1 = m(x - x1)
y - 7 = -1/2(x - (-15))
y - 7 = -1/2(x + 15)
