Number of elements in universal set is n(U)= 23.
Let A, B, C, D be the sets containing people who like only Maths, only English, Maths and English
And who doesn't like maths and English respectively?
People who likes Maths = n(A)+ n (C)
People who likes English = n(B) + n (C)
People who doesn't like Maths and English =n(U)- n(A)-n(B)-n(c)
n(A) + n(C) = 13
n(B) + n(C) =12
1 = 23 - n(A) -n(B) -n(C)
Solving we get n(C) =3