Let f: N → N be a function such that f( m + n )=f( m )+f( n ) for every m, n ∈ N. If f(6)=18, then f(2) · f(3) is equal to:

Let $\displaystyle f: \mathbf{N} \rightarrow \mathbf{N}$ be a function such that $\displaystyle f(\mathrm{~m}+\mathbf{n})=f(\mathrm{~m})+f(\mathbf{n})$ for every $\displaystyle \mathrm{m}, \mathbf{n} \in \mathbf{N}$. If $\displaystyle f(6)=18$, then $\displaystyle f(2) \cdot f(3)$ is equal to :