There are 45 balls in the sports room, 9 are borrowed for the first time, and 10 are borrowed for the second time, how many balls are missing in the sports room?
体育室有45只球，第一次借走9只，第二次借走10只，体育室的球缺少了多少只．
<gadget id="calculator">9 + 10</gadget>
<output>19</output>

<result>19</result>