Step one When getting from a point to another point you always start with the x axis the X axis goes left to right so in order to get point's B&C lined up we need to go to the right 3 points.
Step two Now you need to get B to C by going down on the graph. In order to do so we need to go down 7 points.
Finally you need to write down your answer of First (3) then it was (-7) your final answer is (3,-7)