Question 1011221
This one is perpendicular,{{{y-3=-(1/3)(x+1)}}}, but not yet what you want.


{{{y-3=-x/3-1/3}}}

{{{-3y+9=x+1}}}

{{{-3y=x+1-9}}}

{{{3y=-x+8}}}

{{{y=-x/3+8/3}}}


But the y intercept will be different .... What point do you want this line to pass through?  Your question description is not complete, but you have something {{{y=-x/3+b}}}.  When you know what point is to be included, you can solve for b.