Every year, the United States Federal Trade Commission rates cigarette brands according to their levels of tar and nicotine, substances that are hazardous to smokers’ health. Additionally, the commission includes the amount of carbon monoxide, which is a by-product of burning tobacco that seriously affects the heart. A random sample of 25 brands was taken.

a. Are the levels of tar and nicotine linearly related?

b. Are the levels of nicotine and carbon monoxide linearly related?