A simple random sample of 81 8th graders at a large suburban middle school indicated that 87% of them are involved with some type of after school activity. Find the 90% confidence interval that estimates the proportion of them that are involved in an after school activity. a) O (0.809, 0.931) b) O (0.859, 0.864) c) O (0.809, 0.731) d) O (0.709, 0.881) e) O (0.729, 0.531) f) O None of the above