จาก SMO 2009
 

Let $X=(x_1,x_2,......,x_9)$ be a permutation of the set $\{1,2,\ldots,9\}$ and let $A$ be the set of all such $X$ .
For any $X \in A$, denote $f(X)=x_1+2x_2+\cdots+9x_9$ and $ M=\{f(X)|X \in A \}$. Find $|M|$. ($|S|$ denotes number of members of the set $S$.)