The first thing to do is to look at the points given and decide if you are going to get a negative or positive gradient. We can determine, from inspection that the gradient will be negative because as the x value increases the y value decreases along the line. So we can calculate the gradient m=(y2-y1)/(x2-x1) m=5-2/4-9 m=3/-5 m=-3/5 Now we can calculate the equation of the straight line. y=mx+c pick one of the co-ordinates and sub in their x and y values I'll use (5,4) 4=-3/5*5+c 4=-3+c c=7 y=(-3/5)x+7