You have the following pair of points:
(-8 , 0) and (0,4)
The previous points make part of a line with a certain slope and y-intercept.
In order to determine the equation of the line you use the following formula for the slope of the line:
m = (y2 - y1)/(x2 - x1)
where (x1,y1) and (x2,y2) are two point on the line. You can take these points as the given points (-8 , 0) and (0,4). Then, you replace in the formula for m, just sa follow:
m = (4 - 0)/(0 - (-8)) = 4/8 = 1/2
then, the slope of the line is m=1/2. Next, you use the formula for the m but only using one of the given points, just as follow:
m = (y - y1)/(x - x1) where (x1, y1) is (-8,0)
m = (y - 0)/(x - (-8))
m = y/(x - 8) multiply both sides by (x - 8)
m(x - 8) = y replace m
(1/2)x - (1/2)8 = y
1/2 x - 4 = y
y = 1/2 x - 4
Hence, the equation of the line is y = 1/2 x - 4. The line has a slope of m=1/2 and the y-intercept is -4