Question 884928
{{{x-3y=0}}}
{{{x=3y}}}
{{{y=x/3}}}, the slope is {{{(1/3)}}}.


The slope you want for the line perpendicular to {{{x-3y=0}}} must be {{{-3}}}.  The slopes for perpendicular lines in a plane must be negative reciprocals.


Using SLOPE-INTERCEPT FORM, you want an equation {{{y=-3x+b}}} and you do not yet know b.  You know that the line must pass through (-9,3).
{{{y+3x=b}}}
Substitute the coordinate values.
{{{b=3+3(-9)}}}
{{{b=3-27}}}
{{{b=-24}}}
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Equation in slope-intercept form still, is {{{y=-3x-24}}}.
Convert that into standard form.