Xiaoling can sing 9 songs, Xiaoshan can sing 14 songs, and the two can sing 16 songs in total. How many songs can both of them sing?
小玲会唱9首歌，小珊会唱14首歌，两人一共会唱16首歌．两人都会唱的有多少首．
<gadget id="calculator">14 - 16</gadget>
<output>-2</output>

<gadget id="calculator">9 + (-2)</gadget>
<output>7</output>

<result>7</result>