Answer :
For this case we need to take in count that the equation of a line is given by:
[tex]y=mx+b[/tex]Where m is the slope and b the intercept. We can find the slope with this formula:
[tex]m=\frac{d-0}{0-(-3d)}=\frac{d}{3d}=\frac{1}{3}[/tex]Now we just need to find the intercept. And we can use one point given and we got:
[tex]d=\frac{1}{3}(0)+b[/tex]So then our equation would be:
[tex]y=\frac{1}{3}x+d[/tex]And we can verify that it works
x=-3d y= 1/3 (-3d)+d= -d+d=0
x=0 y= 1/3 (0) +d =d