The students went to the gymnasium to borrow balls. The first class borrowed 9 balls, and the second class borrowed 6 balls. How many balls have been reduced in the gymnasium?
同学们到体育馆借球，一班借了9只，二班借了6只．体育馆的球共减少了几只？
<gadget id="calculator">9 + 6</gadget>
<output>15</output>

<result>15</result>