Select the 'Graph' tab, type in the equation and click on 'Solve'.

The solution is the intersection point of the two lines:

x + 3y = -9

5x + 3y = 3

Zoom in the part of the graph where the intersection is located by selecting the area with the mouse.

You will be able to read the solution from the graph:

Click here to see the graph.

The intersection is (3, -4), that is, the solution is: 

x = 3

y = -4