A radio talk show host with a large audience is interested in the proportion p of adults in his listening area who think the drinking age should be lowered to 18. To find this out he poses the following problem to his listeners: "Do you think that the drinking age should be reduced to 18, in light of the fact that 18-year-olds are eligible for military service?" He asks listeners to phone in and vote "yes" if they agree the drinking age should be lowered and "no" if not. Of the 100 people who phoned in, 70 answered "yes." What is the margin of error for a 90% confidence interval?