Question

If n(A union B)=60, n(A)=30, n(A intersection B)=15,then n(A)=?

Answer 1

Here you did a mistake ,
n(A) is given
n(B) is require

formula,
n(A U B) = n(A) + n(B) -n(A n B)

here,
n(A U B) = 60
n(A ) = 30
n(A n B) = 15
n(B) = ?

now,
60 = 30 + n(B) - 15
n(B) = 45