Flip or buy and hold in Philly? I NEED HELP

[Monet Calvit]

Hello BP members. I need help. I found out today that the house my grandfather left to my aunt when he passed away is still on the market in PA. My aunt has the house priced at $48k and is selling it "as is".  It needs a total rehab. There's currently a tenant in the house that has been there for a really long time paying only $500 in rent per month. My aunt is ready to be done with the property so I thought this would be a great first time investment opportunity for me. Just doing a brief look online, similar houses in that neighborhood are selling for $25-$30k and rehabed houses are on the market for approx. $99,500 to $116,000. The rental rate is between $700 and $900 per month so the curret tenant couldn't stay there paying that amount. I would like to jump on this but I'm really stuck with the calculation part. 

My questions are:

1. Do you think this is a good deal? (Please walk me thru why for either yes or no answers.)

2. If yes, do you recommend I flip or buy and hold? If not, how could I make this a good deal?

3. What equation should I use to determine my ROI for either flipping or buy and hold?

I'll take any insight anyone is willing to offer. 

Thanks