Leakage from underground fuel tanks has been a source of water pollution. In a random sample of 87 gasoline stations, 13 were found to have at least one leaking underground tank.
a. Find a 95% confidence interval for the proportion of gasoline stations with at least one leaking underground tank.
b. How many stations must be sampled so that a 95% confidence interval specifies the proportion to within ±0.03?