ALV- Show column that calculates values after checking a checkbox?

Dear Friends,

I have this problem, I have an alv that does some calculations when I check some of the check boxes but my task is to add one more checkbox and when you check that check box than it should calculate somethin ( in my case add percentage to the original value), how do I do it, how do I write that when I check a checkbox than I get one more column in my alv grid that calculates extra percentage of the original value

I am sorry for my bad english

Thank you in advance