Notice how all of the points in graph B are near to a single line. This is the regression line. We don't have every point on the same line, but it's close enough. Graph A seems to suggest an exponential growth curve could work as the regression curve. Graph C seems to be randomly scattered points, so perhaps no function would work as the regression curve.
I used technology to get the regression line. Specifically, I used GeoGebra. Any spreadsheet program or graphing calculator should be able to find the regression line. You can do so by hand, but I don't recommend it because it's tedious busy work in my opinion.
