What's free? There is no such thing as free electricity unless you build green energy like solar system or wind turbine, if that's from government then it's not free, anyways just know that RX550 isn't Profitable at all, the RX560 is a bit better, it can do 10mh per sec with 45 watts, that's 0.80$ per day
I think RX550 have 4gb GPUs too, you can easily see that using Minerstat calculator, and it says this card can do 11mh/s on Ethereum network, that's not bad, very close to a 1$ right now, OP can still make close to 2$ every 24 hours with these two cards, put them to work already before it's too late