CAN SOMEONE HELP ME FIX THIS FORMULAE: IF {GST Rate}= (g) THEN SUM({Total inc GST}/11, IF {GST Rate}IS BLANK() THEN SUM {{Total inc GST}/0

Can you pls tell me how to write a formular when I have a retail price in a colum and I need to have a colum that is 40% of the retail price.