What is the Hausdorff dimension of the following sets?

a) { (x,x) R^2 : x Q } where R is the real numbers and Q is the rational numbers.

b) { (x,x) R^2 : x R }

c) { (x,x)R^2 : x C } where C is the middle third cantor set.

I think the answer to c) is log2/log3 but i am not sure how to find the other two Hausdorff dimensions.

Thanks.