Calculus
posted by Jose .
The number, N, of people who have heard a rumor spread by mass media by time, t, is given by N(t)=a(1−e−kt). There are 6 million people in the population, who hear the rumor eventually. If 5% of them heard it on the first day, find the percentage of the population who have heard the rumor after 5 days.

what do I use for a and k in this situation? i tried taking the derivative but no answers i come up make sense based on the problem.