Plotting lines and figure question-cftool

Hi I am having trouble with matlab here, I am to find the yield strength from a .txt file of strain and stresses. I can get the data to show up on the cftool window. But I am having trouble getting a linear fit for a certain set of data. Also, I need to plot a line that is .02% offset from the linear fit line. Then I need to find the intersection of the offset line and the data. Lastly, How would I save the graph with all 3 lines as a figure? If you could help me that would be greatly appreciated.

[bym]

maybe you can post some data and what you have done so far