Good old Windows calculator:
Here's some advice on how to ask questions on these forums:
* Try to find the answer for yourself first. For instance, using Google. You do have an Internet connection, don't you?
* If you still can't find the answer, post enough detail that we know what the situation is, why you think it's wrong, etc.
Let me illustrate what "enough detail" means:
I tried to compute the cubic root of -27 in Windows Calculator [version blah] and I get an error message that would translate to "invalid value". Shouldn't the answer be -3? Is this a bug?