You are on a space ship infested with tribbles, an alien species which reproduces exponentially. At the beginning of the infestation, 20 tribbles were on the ship. After 6 hours there were 80 tribbles. a) Write down a formula for N(t), the number of tribbles on the ship at time t hours. b) How many tribbles will be on the ship after 24 hours? c) At what time will there be 500 tribbles on the ship?