Answer:
the slope of each trend line
Explanation:
The rate of change of the variables (dependent and independent) in the linear model is given by the slope or gradient of the regression model usually represented as :
y = bx + c ; where b is the slope and gives the change in y per change in the value of x.
Hence, when intending to find the rate of change of different Datasets, the slope of the trend line corresponding to each dataset is compared in other to determine the identify the differences in the rate of change of each dataset.