(Please show work) Little Green island originally had no turtles. After 55 turtles were introduced to the island, their population is modelled by (View photo) where "a" is a constant and "t" is the time in years since the turtles were introduced. 1. Find the value of "a".

2. Find the time, in years, for the population to decrease to 20 turtles.

3. There is a number "m" beyond which the turtle population will not decrease.
Find the value of "m". Justify your answer.