You can put this solution on YOUR website! graph y=-1/2+ 4
y=3.5 (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, y = 3.5).
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Unless you forgot the x [y=-x/2+4] then: (graph 300x200 pixels, x from -6 to 10, y from -10 to 10, -x/2 +4).