If "Base Qty Sold - Detail" is an integer then the integer division by 9 will return 0 for any value less than 9. So if "Base Qty Sold" = 14 and Detail = 7 the result of subtraction is 7 and then 7 / 9 = 0 with remainder 7. Of course multiplying any value by 0 results in 0.
So I think you need to work on a different approach to the problem.
HTH
The base quantity sold is a varchar field and if the value being divided os less than 9 then it should return a decimal which should be multiplied by the user category value 5 field.