How to make salary field read only when amount is auto populated based on Grade.

Summary:

Hi experts

We have requirement on Add pending worker page in section "Salary" where we want to make salary field read-only when amount is populated based on Grade selected in employment details section and make it editable when User is prompted with salary range based on few grades with min and max salary amounts , so that user can choose salary value. Can anyone help me on this to achieve this logic .

As we have few grades with default amount and few grade with min and max amount values , we need to view only and editable logic based on grades.