The fourth grade students participated in the broadcasting exercise competition. They lined up in 6 rows with the same number of people in each row. Xiaohong was in the 4th row. She was the 9th person from the front and the 12th person from the back. How many people in the fourth grade participated in the competition?
四年级同学参加广播操比赛，他们排成6行，每行人数相同，小红排在第4行，从前面数是第9人，从后面数是第12人．四年级参加比赛的有多少人？
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<gadget id="calculator">9 + 11</gadget>
<output>20</output>

<gadget id="calculator">6 * 20</gadget>
<output>120</output>

<result>120</result>