How to convince my parents to get chickens?

Ok so i really want some pet chickens cause we could keep them in the back yard and eat their eggs. I've done reaserch and now i really want some. Im think about 2-3 with a chicken ark/tractor in the back yard. How do i convince them to let me get them? (sorry about any typos, im on my ipod and turne off auto correct cause it was getting annoying)