For any two sets $\mathrm{A}$ and $\mathrm{B}, \mathrm{n}(\mathrm{A})=15, \mathrm{n}(\mathrm{B})=12, \mathrm{~A} \cap \mathrm{B} \neq \phi$ and $\mathrm{B} \not \subset \mathrm{A}$
Find the minimum possible value of $\mathrm{n}(\mathrm{A} \Delta \mathrm{B})$.
(1) 3
(2) 4
(3) 5
(4) 6