Chapter 7 - Estimates and Sample Sizes - 7-2 Estimating a Population Proportion - Basic Skills and Concepts - Page 337: 12

$0.27-0.087$

$\hat{p}$ is the sample average of the boundaries, hence:$\hat{p}=\frac{(0.27-0.087)+(0.27+0.087)}{2}=0.27.$ E is half of the confidence interval, hence:$E=\frac{(0.27+0.087)+(0.27-0.087)}{2}=0.087$, hence the confidence interval: $0.27-0.087