DFF in Job Offer to appear based on value in another DFF in Job Offer

Summary:

DFF in Job Offer must appear based on value selected in another DFF in Job Offer

Content (required):

We have a DFF (Descriptive Flex Field) that is a Text Box display type field. This DFF must appear on the Job Offer page based on the value selected in the Drop-down List of another DFF in the same Job Offer. Recreation Leave Type is a drop-down list in Job Offer. Only if the recruiter chooses the value 'Casual', the Recreation Leave Weeks DFF must appear in the Job Offer. Recreation Leave Weeks DFF is a text box.

How do we do this in the Descriptive Flex Field configuration? Please help us.