Hello, I am hoping to have help confirming my answer to the below questions a & b.

I believe the correct formula is n = (z/e)2p(1-p), but would appreciate confirming that as well. A thorough walkthrough of how you derived your answer would be much appreciated. Thank you.

An analyst is estimating the percentage of time that a lab technician spends on microscopic examination of blood cultures at the 95.5% confidence level. Lab technicians have previously estimated the proportion to be 25%. a) What sample size would be appropriate to have an error of no more than 4%? b) If a sample of 300 is used, what would be the potential error for the estimate