The company i work for pays $8 an hour more at a different property for the same position i do, how do i go about bringing this up to my boss?

I work for a pretty big retirement community that has multiple properties all around the US. The other day i was just browsing jobs snd stumbled upon my position at a property that is only 30 minutes away from the current one i work at and the job posting stated that the position starts at $23 an hour. I started this job in October of 2018 at $15 and have only got one raise for $.75. I definitely feel like this is unfair considering the job description is exactly what im doing so i was going to ask my boss for a raise but i dont really know how to go about it since in the 5 years ive been working (various jobs) ive never asked for one. Also i should mention that these two properties are in two different states but its only a 30 minute drive from one to the other (without traffic).

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