If n(A) denotes the number of elements in set A and if n(A)=4,n(B)=5 and n(A∩B)=3 then n[(A×B)∩(B×A)]=
If A and B are two sets having 3 elements in common. If n(A) = 5 and n(B) = 4, find n[(A×B) and n(A×B)∩(B×A)].