How to define the cells at last column

Hi experts,

my script like this:

var docs = app.documents;
    for (var i = docs.length-1; i >= 0; i--) {
            var myCells = docs.stories.everyItem().tables.everyItem().cells.everyItem().getElements();  
            for(var n = 0; n < myCells.length; n++)  
            {  
                var mCellStyles = docs.allCellStyles;
                    if (/^9[9876]/.test (myCells.appliedCellStyle.name)) {  
                            myCells.contents = " ";  
                            var myRow = myCells.parent.rows;
                                    myRow.cells[-1].rightInset ="2 mm";
                      }  
                }  
            }

aim to let last column of cells if the cell applied cell style 96 97 98 99, rightInset ="2 mm";

but not working,

could someone please show me how.

thanks

regard

John