Answer:
y=-x/3+2
Explanation:
If you graph out 3x-y-7=0, you will get a line that goes through the points (0, -7), and about (2.3, 0). If you graph out y=x/3+2, you have to make sure that this line forms a 90 degree angle on the previous line, thus making this line perpendicular to the previous line.