In order to calculate gradient is is the following : m = Vertical distance / Horizontal distance. These distances can be found out by drawing a line from any point on the line until it will line up with another part of the line at a definitive point, and then going up/down to this point.
Try use these to help you with your answer, you've worded it a bit weirdly.. If you have a picture of the graph I can figure it out easier.
