The slope-intercept form of a line is:
y = mx + b
where m is the slope and b the y-intercept
The slope of a line that passes through points (x1, y1) and (x2, y2) is computed as follows:
Replacing with (4, 4) and (20, 12):
Replacing into the general equation with m = 1/2 and point (20,12) we get:
12 = 1/2(20) + b
12 = 10 + b
12 - 10 = b
2 = b
Then, the equation is: y = 1/2x+ 2
And the graph is: