Assuming the line passes through the points (0, -2) and (4,0)
First, begin by finding the slope;
m=

m=(0-(-2))/(4-0)
m=2/4
m=1/2
Now write this into the equation y=mx+c;
y=(1/2)x+b <-- put in coordinates of a point to find b
-2=(1/2)(0)+b
b=-2
The final equation is y=1/2x-2
Hope I helped :)