Hello @Nur Fadhilah Binte Mohamad Noor
Firstly, you need to convert Attribute ValueZ from AutoNumber to an Integer. This is because A + 100 is an integer and not an autonumber.
Secondly, there are various ways to achieve A + 100 = Z. I have mentioned one such method below:
1. You can have a popup page where the user can fill in the value for attribute A
2. Then you can have a OnChange event to the text box of attribute A which calls a nanoflow
3. In the nanoflow, you can have a change object activity for entity "FIrstMilestone". In that change the value of ValueZ as ValueA + 100. This will store the sum in ValueZ.
4. Later you can show the value of ValueZ to the user to confirm the summation
Hope this was clear to you
Generally you: