What happens next?

How to convince parents to let you get a gerbil
Get on the internet or go to your library and research all about gerbils :
Feeding habits, bathroom habits, how much you'll need to do to take care of them, etc. Gerbils are among the longest-lived and cleanest of common rodent pets. Also, get some really cute pictures of gerbils.
Find out where you can get a gerbil and all the things it will need. Learn how much everything will cost and include that in your presentation.