Difficult probability question S1

Hi,

P(A) = 0.4 and P(A u B) = 0.7

Find:

a) The P(A' n B)
b) The P(B) if A and B are mutually exclusive
c) The P(B) if A and B are independent.

I think a) is 0.3 and so is b)... but I'm not sure on c)

I know then P(A n B) = P(A) x P(B) but I can't work out P(B)!! I know that the probability of B without the intersect is 0.3...

Help me!!
Thanks!!