In this scenario, the calculated field Allowable Days and the Required Delivery Date need to display on the project. To achieve this:
Allowable Days: This is a calculated field, so it should be set up as a calculated field in the project custom form, which references the difference between the Request Entry Date and the Required Delivery Date.
Required Delivery Date: This is a static field and should be displayed as a text field to ensure that the original requested delivery date is retained.
Option B is incorrect because both fields do not need to be calculated. The Required Delivery Date is already a static value and doesn't require calculation.
For more information, refer to the Workfront documentation on setting up calculated fields and text fields in custom forms.