How do i convince my mom to let me have a hamster?

my aunt went to holiday world with my uncle my 2 cousins and her and my mom and i had babysat her dog i did most of the work i fed him i took him one walks played with him and they picked him up a couple of hours ago and i think it showed how responsible i am and the dog was a pit bull a pup tho but still how do i convince my mom to let me have a hamster help