a.) For what choice of p are A and B mutually exclusive events?

b.) For what choice of p are A and B independent events?

I know P(A U B) = P(A) + P(B) - P(A ∩ B) thus P(A ∩ B) = 0.4 + P(B)-0.7 but I don't know how I would find P(A ∩ B) without knowing P(B)