When is integrating using the tabular method useful?

please show work

Suppose I have run the simple linear reggression model through R code based on Data file(name is DATA) which has 30 line data. Now I need plot and run the simple linear reggression model through R code based on same Data file with only 1 to 20 lines data. If I wrote the code : Data2=[1:20], then use plot(), lm(), fit() commands. cant work it How to write the R code for the second simple linear reggression mode ? thanks for your help.

14) The equation of the least squares regression line between the dose of medication in mg (x) and the patients' systolic blood pressure (y) is... ŷ = -10x + 170 a) Use the regression line to estimate the systolic blood pressure for a patient taking 4 mg of medication. b) If we want to have a systolic blood pressure of 110, use the regression line to estimate the appropriate dose.