Calculating change between two trend lines in one data set...

[Last_Taste]

Hello,
I am trying to correctly calculate “percent change” or change over time in a data set with two trend lines. Percent change is in quotes, since that may not be the correct term. I am using a scatter plot to examine the relationship between an independent and dependent variable. Where the relationship changes, the slope of the line changes.

I have plotted out two trends lines with equations and R2 values. Can I use the “m” values form the Y=mx+b equations to calculate the change in the relationship?

I have included an example.

Thanks!