As Taylor and Kristen have said, the key to solving this problem is to understand that when you subtract a negative number, you are doing the same thing as adding a positive number, so "-(-34)" is the same as +34. The two ways I suggest you remember this are:
1) Visually: when you have two minus signs, turn one of them sideways and put it on top of the other; you will get a plus sign. This works for any number of minus signs; if you have an even number of minus signs they will all make plus signs and you add, but if you have an odd number of plus signs, you will always have one minus sign left over at the end so you subtract. This isn't a mathematical proof, but it is a handy way to remember what to do with more than one minus sign.
2) Think about money: negative money is debt; if you have -$34, you owe 34 dollars. Subtraction is taking away, so if you subtract -$34 (ie "-(-34)"), then you are taking away $34 of debt. Taking away debt is the same thing as adding money; if you owe me $5, and I give you $5 as a gift to pay your debt back to me, that is the same thing as if I just forgave your debt.
Hopefully you will be able to keep at least one of those strategies in mind, and this type of problem will become easy for you.