Based on your question and based on the graph that you show. I conclude and get an answer that the vertex of the graph is (1,3) and the answer to your second question is maximum. I hope i answer your question directly
I know this because the vertex is on top. and the vertex on the graph is at the point (1,3). I found this out by: looking at the graph and seeing where the vertex lies, and plotting each point to see which one the vertex is on.