Sets

If A and B are two events, such that $P(A\cup B)=\dfrac{3}{4},P(A\cap B)=\dfrac{1}{4},P\left( A^{c} \right)=\dfrac{2}{3}$ where $A^{c}$ stands for the complementary event of $A$, then $P(B)$ is given by:

If $n(A)=4, n(B)=2$. Then the number of subsets of the set $A \times B$ each having at least 3 elements are