If P(A) = 0.2, P(A|B) = 0.3, P(A u B) = 0.4. Find P(B).

Reminding you that:

P(A n B) = P(A) + P(B) - P(A u B)

P(A u B) = P(A) + P(B) - P(A n B)

& that P(A|B) = P(A n B) / P(B)

I think I've got to use simultaneous equations... I just can't figure out where.

Any help? Please show working.

Thanks