ANDROID: How to put an image on the bottom third of a button

I am trying to make a small game that has different levels. For each level, if you beat it you will be awarded a number of stars. How should I display these stars at the bottom on the level?

If the level has not been completed, no stars would appear, but if the level was completed I want to add an image (one with one star, one with two, and one with three) to the bottom of my level # button.

Thanks for any help !