Matrix Calc

Hi To All,

I am developing a user screen.. there are two columns in matrix... Column A and Column B.... when i entered 2 in Column A, the same should be displayed in Column B.. same as when i entered 4 in the next row of Column A, (Both the values 2 and 4 should be added) 6 should be displayed in the next row of Column B..... How to do this.... Values Should be added in the GOT_FOCUS....