Help choosing correct RAM stick

Hello guys. Let me be short, I need to buy one memory stick for my computer. I currently have this one:


My motherboard is a Dell 0gdg8y. I'm going crazy searching for a stick that will be compatible and I just can't seem to find one. I'm no expert in computers so I'm reading a lot. I don't mind buying one from a different brand.

1st question: In order for the sticks to work together, they must have the same Frenquency, Latency and the DDR type right ?

2nd question: As the picture show: "PC3-10600U-10-09-A0". The other stick must have the same specifications?

3rd question: I found some perfect sticks with good prices that could work, the only thing is, they are 2Rx8. I was reading and someplaces were saying that I shoudn't use because they wouldn't work together so well, and some other places were saying that I could use with no problem whatsoever. So, can I use them or not? Brazilian forums are way too confusing so I'm asking here.

Thank you for the help!

Hi go here and have it scan your computer or just manually put your make and model and it will bring up memory that is compatible with your computer they grantee it. http://www.crucial.com/usa/en/memory...ry-_-us-memory