Independent random samples of ash trees from two neighboring areas - one urban and one rural - are examined to see if there is a difference in the proportion of trees showing signs of emerald ash borer infestation. Of the 280 urban trees examined, 28 show signs of infestation and 38 of the 152 rural show signs of infestation. What is the approximate standard error you would use to construct a 95% condence interval for the difference in the proportion of trees showing signs of emerald ash borer infestation using this sample data? [do not round intermediate calculations and round your final answer to 3 decimal places)