How Can i Set negative marking formula in Quize application using Android studio

Hi i am newer in Programing. Anyone Please Help Me. I have a Quize exam Mobile Application developed by Android Studio .i am try to negative marking feature add in my quize application.This Quize Application Have 4 different Question Where 1 Question is Correct & Others 3 Different question is wrong. Now i want to.... *if user Clicked Right Answer He/She will Get 1 mark Per Question. But if User clicked Wrong answer He/She Will get per question (-0.5) Mark And this mines Mark is mines from total mark. *How can i make this formula in Android studio. Thank you So much.