Adding Numeric fields together

I have added another NumericField (4) to a form and want to calculate it with the 'total' numericField only, ie

NumericField 1

NumericField 2

NumericField 3 - this is 15% of the total of NF1 & 2

NumericField 4 - this is to exclude the 15% and then be added to the Total

NumericField 5 - Total of all the above

I don't seem to be able to get field 4 to adjust the Total when I add a value. How would I change it

the script for NumericField5 is: event.value=NumericField1.rawValue+NumericField2.rawValue+NumericField3.rawValue

(using Livecycle Designer ES 8.2)

Thank you