Answer :

Correct answer is : 15

n(A) = m, then number of subsets of A = 2^m

n(B) = n, then number of subsets of B = 2ⁿ given that

2^m – 2ⁿ = 56

2^m – 2ⁿ = 26 – 23

From here, m = 6

n = 3

2m + n = 2 × 6 + 3 = 15