How do I update a Task field automatically?

How do I update a Task field automatically?

Hi Brains Trust,

I have created a new field called Estimated Hours (number).
I have created a checkbox field called Included.

For some projects we may 'Include' various tasks, if checked, we want the Estimated Hours to be updated to have the Duration hours reflected.

I am familiar with Workflows in Zoho CRM, but cannot seem to find similar functionality in Projects.

Thanks

Steve