In order to graph each equation, we need to choose two points that are solution of each equation.
To do so, we just need to choose a value of x and then calculate the corresponding value of x.
So for y = x + 6, we have:

Now, for y = -2x - 3, we have:

Graphing the points and the corresponding lines, we have:
To calculate the solution of the system of equations, we can equate both values of y from each equation:

So the solution is the ordered pair (-3, 3).