3. (3 points) There is a mathematical operation symbol “ $\odot$ ” that makes the following equations true: $2 \odot 4=8, 4 \odot 6=14, 5 \odot 3=13, 8 \odot 7=23$. According to this rule, $9 \odot 3=$ $\qquad$
3. (3 points) There is a mathematical operation symbol “ $\odot$ ”, which makes the following equations true: $2 \odot 4=8,4 \odot 6=14,5 \odot 3=13$,
$8 \odot 7=23$. According to this rule, $9 \odot 3=$ $\qquad$ .

【Solution】Solution: $9 \odot 3=9 \times 2+3=21$;
Therefore, the answer is: 21.