There are 3 rows of small cars parked in Ping An parking lot, with 6 cars in each row; 9 large cars parked in each row. How many more small cars than big cars.
平安停车场停了3排小汽车，每排有6辆；大汽车停了9辆．小汽车比大汽车多多少辆．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 - 9</gadget>
<output>9</output>

<result>9</result>