The slope of the line is .02
In order to find the slope, you need to pick two points that are both on the line. Then you can use the slope formula you included. Two points that are on the line are (500, 35) and (1250, 50). Now we plug into that equation.
(y2-y1) / (x2-x1)
(50 - 35) / (1250 - 500)
15/750
.02
