In a 2018 study reported in The Lancet, Mercie et al. investigated the efficacy and safety of varenicline for smoking cessation in people living with HIV. The study was a randomized, double-blind, placebo-controlled trial. Of the 123 subjects treated with varenicline, 18 abstained from smoking for the entire 48-week study period. Of the 124 subjects assigned to the placebo group, 8 abstained from smoking for the entire study period.

a. Find the sample percentage of subjects in each group who abstained from smoking for the entire study period.

b. Determine whether varenicline is effective in reducing smoking among HIV patients. Note that this means we should test if the proportion of the varenicline group who abstained from smoking for the entire study period is significantly greater than that of the placebo group. Use a significance level of 0.05.