Hello

The document you referenced applies to numerical values not expressions containing field operations.

For the first syntax error, just use 0 - entity.TimeSpent_c ...

As for why the expression doesn't work, it depends what RelatedRecordsRequest_c is. If it is a MANY2MANY relationship, you cannot use it, as it's a pointer vs a collection, not a field. If it is an ENTITY_LINK, make sure all the relevant fields are not null (RelatedRecordsRequest_c. ToplamEfor_c . TimeSpent_c).

Best regards,

Brindusa

entity.RelatedRecordsRequest_c is Entity Link refer to Request and RelatedRecordsRequest_c.ToplamEfor_c is double. 

entity.TimeSpent_c is double. 

Then the second expression should work, assuming all fields have a valid value (not null). What do you see if you run the workflow debugger? Is it possible you have an error you don't see in the UI because it is on the related record?
For testing purposes, could you please add the rule on an After change event? Just to avoid any interaction with the actual record deletion.By the way, what is the use case for deleting a record? I would assume from a business logic it is better to inactivate a record rather than delete it (losing all traceability and potentially having dangling "pointers").

hello brindusa , I wrote this rule in custom transition instead of before deleting. the rule in transition worked. i can't understand why it didn't work in before deleting phase

It could be a timing issue, since you are interacting with another record, by the time the record gets updated, the related record may already be deleted and the info not available to reference.

Hi brindusa , I tried this. instead of setting the time, I tested it with options such as update the description of a record or change the company information of a person. it was successful in these tests. but it failed to make the above time calculation.

If you run the workflow debugger, do you get any additional information? Do you see an error or not what you expect when the expression is evaluated?

I made another alternative solution, thank you.