Question 934052
It's a linear equation so you need two points. 
Easiest way is to plot the intercepts.
When {{{x=0}}}
{{{0+3y=12}}}
{{{3y=12}}}
{{{y=4}}}
(0,4) is one point.
When {{{y=0}}}
{{{x+3(0)=12}}}
{{{x=12}}}
(12,0) is another point.
Plot those two point.
{{{drawing(300,300,-2,14,-8,8,grid(1),circle(0,4,0.3),circle(12,0,0.3))}}}
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.
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Then draw the straight line between them,
{{{drawing(300,300,-2,14,-8,8,grid(1),circle(0,4,0.3),circle(12,0,0.3),graph(300,300,-2,14,-8,8,(12-x)/3)))}}}