Return on investment

[Franco Epifania]

So its been about 4 months since I’ve purchased this 3 family and so far so good. I put 105k down & I net around 1600/month. Not sure if I calculated the ROI correctly, basically to what i would net in rental income in a year and divided it by my outnof pocket costs which was around 110k. Is this he correct way to calculate? Sounds stupid but still new to investing and I’m aleays rehinking everything.