Adding to my program features

I need help with my small application. I am programming a local based game using Google Maps, current location and marks with radius, which will allow user to start new activity when he is there. What I need? I need implement to my code markers with radius. The possition of them is based on longtitude and latitude which you will gave just example there. Another thing that must be circle arround them. Cause The point of game is to get to mark possition and start some game. So when the player get to radious and click on marker the applicatioun start new activity with game. After he finish the game mark must dissapear. What I have done? I have implemented Google api and working current possition system, some activities. How much time you have? In case that it is easy work It need to be done today.