4 plex operating expenses with 50% vacancy

[Akash Acharya]

There is a nice 4 plex that I am currently looking to buy at some point that costs $510k. It's located in Atlanta and is only 50% occupied. It has 3 2bd 2bth(rent is between $2700 to $2800 a month) and 1 1bd 1bth(rent is $1700 per month). The property listing says that with a 50% occupancy the gross annual income was $49,700. Total taxes were $4k and total operating expenses were $15k. With total net income at $30,700. My question is if the property was 100% occupied would the operating expenses go up or stay the exact same? And if so would this be a property worth buying?