There are 5 boxes of ping pong balls in the store, each box has 8 balls, and 15 balls are sold, how many are left?
商店里有5盒乒乓球，每盒8个，卖出15个，还剩多少个？
<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<gadget id="calculator">40 - 15</gadget>
<output>25</output>

<result>25</result>