From my general chemistry studies, I know that exponential growth and decay can be modelled by:
, where A is the starting amount, k is just a constant, and t is the time.
I will show you #2 and then you will be able to do #1.
Your information indicates terminating mass as 27 g, A = 216 g, and t = 27 min:
I hope that this helps. Be sure to write back for more help.