Two finite sets have m and n elements respectively.

Solution:

Let us suppose two finite sets are A and B
Let A has m elements

Let B has n elements

Then total number of subjects of A is 2m and total number of subjects of B is 2n.

According to given condition,

2m – 2n = 56

i.e 2n (2m – n – 1) = 56

Since 56 = 8 × 7

$=2^{3} \times 7$

i.e. $2^{n}\left(2^{m-n}-1\right)=2^{3} \times 7$

i.e $n=3$ and $2^{m-n}-1=7$

i.e $2^{m-n}=8$

$2^{m-n}=2^{3}$

i.e. m – n = 3

i.e m = n + 3

m = 6

i.e m = 6, n = 3

Hence, the correct answer is option C.