Answer
$$y= -\frac{1}{3}x+b$$
Work Step by Step
The line perpendicular to the line with slope $m$ has slope $m'$, where $$m'= - \frac{1}{m}.$$The lines in Exercise 1 have slope $m=3$, so any line perpendicular to those lines has slope $m=-\frac{1}{3}$.
The equation for the family lines whose members have slope $m$ is$$y=mx+b,$$so the equation for the family lines whose members are perpendicular to those in Exercise 1 is$$y= -\frac{1}{3}x+b.$$
