# Understanding the lower and upper limit of a graph

I was recently presented the following graph:

I was given very little context and I have to recreate it. I don't want it to be done for me, but some context would help.

Any idea what these upper and lower limits represent? Are they represented by an exponential function (I noticed the lines curve)? Or is there some value at each point (it doesn't seem like it the way they are drawn)? I think it has something to do with error or confidence level?

I'm able to represent the data points in excel, and make a line of best fit, but have no idea what the dotted lines represent, or how to add them to my excel graph. Any help would be great.

For your data, the bands are given by $$y_\pm=80.3865 x+244.289\pm k \sqrt{80.4453 x^2-8205.42 x+766241.}$$ where $$k$$ depends on the confidence level.