The data listed in the following table are from a study by Benignus and others (1981). Blood and brain levels of toluene (a commonly used solvent) were measured in rats following a 3-hour inhalation exposure to 50, 100, 500, or 1,000 parts per million (ppm) toluene (PPM_TOLU). Blood toluene (BLOODTOL) is expressed in parts per million, weight in grams, and age in days.

a. Provide a scatter diagram, with BLOODTOL as the response and PPM_TOLU as the predictor.
b. Compute least-squares estimates of the straight-line regression coefficients. Plot the line on the scatter diagram.
c. Repeat part (a) for the natural logarithms LN_BLDTL and LN_PPMTL, the respective natural logarithms of BLOODTOL and PPM_TOLU.
d. Repeat part (b) for the natural logarithms.
e. Which transformation leads to the best representation of the data? Note in your comments the validity of the regression assumptions.