How to check current rent market for 1 unit in a triplex?

[Vinh Nguyen]

Hi, we just purchased a triplex with a tenant occupying one of the units; she has been there over 10 years. We are looking to increase the rent. Based on what someone suggested here, I should present to the tenant the current rent market for her unit and offer a discount in order to ease the bad news. What is a way to provide such document to the tenant to show her that we are not purposely giving her a hard time? her lease is due in April.