The easiest way, I believe for this problem is that you first complete the square, ie get it in the form of
Then (b, c) becomes your vertex and you can easily sketch the graph, by looking for the appropriate intercepts.
or maybe (b,-c), but that is the idea.
You never will find the vertex of the parabola unless you make some effort. I seriously doubt this problem dropped out of the sky and hit you on the head. I am almost certain there was a lecture or a section in book right before you encountered this problem. There was that Algebra I class, however long ago, where you discussed "Completing the Square". All these things can work for your good.