Please help me

A researcher is interested in determining the proportion of first year university students who have suffered hearing loss from loud music and other big-city sounds. How many students should she give hearing tests to, in order to determine this proportion with a margin of error (half width of confidence interval) of 0.14 using a 95% condence interval? a.) If she believes from previous studies that the true proportion is 0.2. (Give answer as a whole number ) [:] b.) If she has no idea of the proportion with hearing loss. (Give answer as a whole number.) [:] mesa/s