Among the 100 foreign language teachers, there are 75 who know English and 45 who know Japanese. How many teachers only know English?
在100位外语教师中，懂英语的有75人，懂日语的有45人，只懂英语的教师有多少人？
<gadget id="calculator">45 - 100</gadget>
<output>-55</output>

<gadget id="calculator">75 + (-55)</gadget>
<output>20</output>

<gadget id="calculator">75 - 20</gadget>
<output>55</output>

<result>55</result>