How to determine the storage on my iphone?

So, my friend gave me her old iPhone, because she got a new one and when she switched her phone over they factory reset this phone. So I'm not able to use this phone because I have verizon and its a at&t phone, which I didn't think about when she gave it to me. I even asked her what size the storage is on this phone and she forgot. It's a 4 gs iPhone and I was just wondering if there's a possibility of figuring out the storage without actually having to be able to get into the phone. I need to know because I'm just going to sell it and get one from my carrier. I already know you guys are thinking "well why not just give her the phone back so she can have the money?" and yes I already asked her if she wanted to do that, and she said no, she doesn't care. If anyone can help me figure this out I would appreciate it!

Plug it into your computer

1. Go to settings
2. Go to general
3. Go to usage and it shows your storage