It would be helpful to see the graph, however, to find the equation, take points off the graph and solve this equation to find out the "M" (slope) variable( y=Mx+B),
y² - y¹ ÷ x² - x¹ = the slope of the line. Based on the fact this is middle school mathematics, I'm hoping this solves your problem. If not, please let me know!
For reference,
Y¹ and Y² would be the position of the points on the Y axis, and the X¹ and X² would be the position of the point on the X axis.
