For y=3x+4, you would put 4 on the y-intercept and from that point you go up 3 and right 1 and then plot the second point.
For y=-x-4, you would put -4 on the y-intercept and from that point go down 1 and right 1 and then plot the second point.
The answer is going to be x=7
A. axis of symmetry: vertex: (–0.5, –0.5)
