Please show me how you solved problem below:
A member of Congress wants to determine her popularity in a certain part of the state. She indicates that the proportion of voters who will vote for her must be estimated within plus or minus 2 percent of the population proportion. Further, the 0.95 degree of confidence is to be used. In past elections, the representative received 40 percent of the popular vote in that area of the state. She doubts whether it has changed much. How many registered voters should be sampled?
a.864
b5200
c.2305
d.2000