The school launched a table tennis competition in the new semester. In order to meet the needs of this activity, the school bought back 7 boxes of table tennis balls, 6 in each box. After using some, there were 23 left. How many table tennis balls were used?
新学期学校开展了乒乓球比赛活动，学校为了满足这次活动的需要，买回7盒乒乓球，每盒6个，用去一些后还剩23个，用去了多少个乒乓球？
<gadget id="calculator">7 * 6</gadget>
<output>42</output>

<gadget id="calculator">42 - 23</gadget>
<output>19</output>

<result>19</result>