Question 172454
For purposes of my response to your question, I am ssuming that the graph is a straight line.  The standard form for the equation of a straight line is 
y = m*x + b  where m is the slope of the line and b is the y-intercept.

To calculate the slope of the line, select two from from the graph of the line. The points should be in ordered pair form i.e. {x1,y1}.  The slope "m" is calculated from the two pairs of points that you have selected.  

m = (y1 - y1)/(x2-x1)

The y-intercept "B" is determined from the from the graph by selecting the value for "y" when x = 0.

{{{ graph( 200, 200, -10, 10, -10, 10, 2x-5 ) }}} 

In this case, the slope is 2 and the y intercept is -5