Please check my math

[Trisha Kirby]

https://imgur.com/a/NkMC65J

I am considering house hacking by buying a duplex to live on one side for about 3 years. To purchase it, I would be using equity from my primary home which I plan on renting out. I think I can save about $9k a year by doing this. 

But I wonder if I am missing something. I am new to this.

The costs you see for the duplex include the heloc and mortgage costs.