x + 3y = 12
This an equation of a line, then we will rewrite as a function of x.
==> y= (12-x)/3
Now when x = 12 ==> y= 0 ==> (12,0) is one point of the line.
==> when x = 0 ==> y= 4 ==> (0, 4) is another point of the line.
We dot both points and connect a line between the,
The graph shown below (black line)
x^2 + y^2 = 9
This equation is an equation of a circle whose center is (0, 0) and radius 3.
Then, we will draw a circle whose center in the origin point and passe through the point (3,0) , (-3,0), (0,-3) , and (0,3).
The graph is shown below as a red circle.
We notice that the line and the circle do not intersect.
Therefore, there are NO solution.