Question 52310
This is a line.  With lines you only need to plot two points and connect them unless you're asked for more.
If x=0
3(0)+3y=12
0+3y=12
3y=12
3y/3=12/3
y=4
Plot the point (0,4).
If y=0
3x+3(0)=12
3x+0=12
3x=12
3x/3=12/3
x=4
Plot the point (4,0).
Connect the dots and you'll get something that looks like this:
{{{graph(300,200,-10,10,-10,10,-x+4)}}}