How to find the difference amount using IF condition in webi

Hello,

Can you please help me on my below scenario

I have a column,, Gross Amount. For eg,

ID        Gross Amt

------     --------------

1          5000

2          20000

3          15000

4          3000

I want to add a new Variable on my webi report as column “Tot Fed”. The requirement is to display if Gross Amt Greater than or equal to 10000, I should display the difference Amount. For eg, please find the expected output from above table for column “Tot Fed”

ID        Gross Amt       Tot Fed

------     --------------      ----------

1          5000                0         

2          20000              10000

3          15000              5000

4          3000                0

I tried with If statement, but I am struck on showing difference amount

Thanks for the Help !!!