The belt used by Dad has a distance of 3 cm between each two holes. Before weight loss, he used the sixth hole. After weight loss, he used the third hole. How many centimeters did his waist decrease?
爸爸使用的皮带，每两孔间相隔3厘米，健身减肥前他使用第6个孔，减肥后，他使用第3个孔，他的腰围减少了多少厘米？
<gadget id="calculator">6 - 3</gadget>
<output>3</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<result>9</result>