Hello @EllenB89267 ,
You won't be able to "merge" a greeting tag or contact details really. In this case I'd recommend either setting it up as inserting a Greeting Tag and inserting a Contact Detail, or to have them both be contact details - i.e. type out the "Dear" then insert the contact details one after another [contact name][contact year].
If you haven't added a custom field for your contacts that includes the graduation year, you'll want to set that up so it can be an option in the email builder. Custom fields can be added via the My Settings page, through a specific contact's pop-up window, or when uploading contact info through a file.
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