Help with variables, please

I have made a promotional game for my band and I need a little help with the scoring.

I have a variable set up for the number of objects hit and the number of shots fired. I want to average the two together to get accuracy.

I have it set up as (just for example):

[color=Orange]//an example of how i am tracking the scoring[/color]
[color=Red] _root.shots += 1;[/color]
[color=Orange] //and then I declare[/color]
[color=Red] shots += 0;[/color]

I am basically just wanting to subtract

[color=Red]_root.score[/color]* from* [color=Red]_root.shots[/color]

I am still pretty new at this. I tried a few different ways and now I am tapped out. If anyone has any ideas on how to make this work I would be greatfull.