Adding days to a date based on drop down menu [Solved/Closed]

Registration date
Saturday August 25, 2018
Last seen
August 25, 2018
Column D shows Date Enrolled, Column E shows Experience (options are more than 1 year or Less than 1 year) I would like column F to add 35 days if "Less than 1 year" and 21 days if "More than 1 year" is selected.
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