Provide an Appropriate Response $99 \%$ Confident That the Sample Proportion Will Not Differ from the to Estimate

Provide an appropriate response.
-A state highway patrol official wishes to estimate the number of legally intoxicated drivers on a certain road.
a) How large a sample is needed in order to be $99 \%$ confident that the sample proportion will not differ from the true proportion by more than $2 \%$ ?
b) Repeat part (a) assuming previous studies found that $80 \%$ of the drivers on this road are legally intoxicated.