Answer :

You need more information than that to solve for x and y.  However, it is possible for you to graph the equation and see what all the possible values for x and y can be.  A possible coordinate can be x=3 and y=3.
I'm not sure what you need to solve for, so I'll solve for both x and y.

                3x + 6y = 27
                        3x = 27 - 6y
                          x = (27 - 6y)/3
                          x = 9 - 2y
so there's x
                 3x + 6y = 27
                        6y = 27 - 3x
                          y = (27 - 3x)/6
                          y = 4.5 - .5x
And there's y