please help with question a and b

9.1.37 Question Help A researcher wishes to estimate the percentage of adults who support abolishing the penny. What size sample should be obtained if he wishes the estimate to be within 4 percentage points with 95% confidence if (a) he uses a previous estimate of 25%? (b) he does not use any prior estimates? Click here to view the standard normal distribution table (page 1). Click here to view the standard normal distribution table (page 2).