If the graph is represented by y=mx+a, then putting in m=-1/2 we have y=-x/2+a; putting in x=0 and y=2 we see that a=2, so the line equation is y=-x/2+2. The y intercept is 2 and the x intercept is when y=0, so x/2=2 and x=4. To graph the line, mark (0,2) and (4,0) on the axes and draw a line through these two points.