State the term used to describe two events $X$ and $Y$ when $P(X\cap Y)=0$.

The events $A$ and $B$ are independent with $P(A)=\frac{2}{3}$ and $P(A\cup B)=\frac{4}{5}$.

Find

$P(B)$

$P(A\cap B^{\prime })$

$P(A^{\prime }|B)$