Using it's formula, it is found that the confidence interval for the percentage of the population that favors the plan is (39.5%, 44.5%).
In this problem:
42 - 2.5 = 39.5%
42 + 2.5 = 44.5%
Hence, the confidence interval for the percentage of the population that favors the plan is (39.5%, 44.5%).
You can learn more about a confidence interval at https://brainly.com/question/25779324