Apps Doing calculations

[Booocubs]

I'm creating a VERY simple application for android, for a game (Ogame).
Now I may add on to this application, but for now this is all I want it to do;

- The user Inputs their level, 
     - If the user inputs < 5000... 
          - It multiplies the number by 5 to get the max 
          - It multiplies the number by .2 to get the min 
     - If the user inputs 5000 < X < 24999 
          - It multiplies the number by .2 to get the min 
     - If the user inputs >25000  
          - It just displays "You can attack anyone > 5000"

My question is; how do you use variables (Such as input = X) and then from there us that X in equations to create an output?

 

[miXer]

You should have a good grasp of Java developing before diving into android development. For this i can recommend this book: Amazon.com: Head First Java, 2nd Edition (9780596009205): Kathy Sierra, Bert Bates, Bert Bates: Books